Fixed modifier code, removed instances of "0 ID = no mon"

src/battle-scene.ts

@@ -932,7 +932,16 @@ export default class BattleScene extends SceneBase {
     return activeOnly ? this.infoToggles.filter(t => t?.isActive()) : this.infoToggles;
   }
 
-  getPokemonById(pokemonId: number): Pokemon | null {
+  /**
+   * Return the {@linkcode Pokemon} associated with a given ID.
+   * @param pokemonId - The ID whose Pokemon will be retrieved.
+   * @returns The {@linkcode Pokemon} associated with the given id.
+   * Returns `null` if the ID is `undefined` or not present in either party.
+   */
+  getPokemonById(pokemonId: number | undefined): Pokemon | null {
+    if (isNullOrUndefined(pokemonId)) {
+      return null;
+    }
     const findInParty = (party: Pokemon[]) => party.find(p => p.id === pokemonId);
     return (findInParty(this.getPlayerParty()) || findInParty(this.getEnemyParty())) ?? null;
   }
@@ -3033,14 +3042,14 @@ export default class BattleScene extends SceneBase {
    * If the recepient already has the maximum amount allowed for this item, the transfer is cancelled.
    * The quantity to transfer is automatically capped at how much the recepient can take before reaching the maximum stack size for the item.
    * A transfer that moves a quantity smaller than what is specified in the transferQuantity parameter is still considered successful.
-   * @param itemModifier {@linkcode PokemonHeldItemModifier} item to transfer (represents the whole stack)
+   * @param itemModifier - {@linkcode PokemonHeldItemModifier} to transfer (represents whole stack)
-   * @param target {@linkcode Pokemon} recepient in this transfer
+   * @param target - Recipient {@linkcode Pokemon} recieving items
-   * @param playSound `true` to play a sound when transferring the item
+   * @param playSound - Whether to play a sound when transferring the item
-   * @param transferQuantity How many items of the stack to transfer. Optional, defaults to `1`
+   * @param transferQuantity - How many items of the stack to transfer. Optional, defaults to `1`
-   * @param instant ??? (Optional)
+   * @param instant - ??? (Optional)
-   * @param ignoreUpdate ??? (Optional)
+   * @param ignoreUpdate - ??? (Optional)
-   * @param itemLost If `true`, treat the item's current holder as losing the item (for now, this simply enables Unburden). Default is `true`.
+   * @param itemLost - Whether to treat the item's current holder as losing the item (for now, this simply enables Unburden). Default: `true`.
-   * @returns `true` if the transfer was successful
+   * @returns Whether the transfer was successful
    */
   tryTransferHeldItemModifier(
     itemModifier: PokemonHeldItemModifier,
@@ -3051,106 +3060,107 @@ export default class BattleScene extends SceneBase {
     ignoreUpdate?: boolean,
     itemLost = true,
   ): boolean {
-    const source = itemModifier.pokemonId ? itemModifier.getPokemon() : null;
+    const source = itemModifier.getPokemon();
-    const cancelled = new BooleanHolder(false);
+    // Check if source even exists and error if not.
+    // Almost certainly redundant due to checking inside condition, but better log twice than not at all
+    if (isNullOrUndefined(source)) {
+      console.error(
+        `Pokemon ${target.getNameToRender()} tried to transfer %d items from nonexistent source; item: `,
+        transferQuantity,
+        itemModifier,
+      );
+      return false;
+    }
 
+    // Check for effects that might block us from stealing
+    const cancelled = new BooleanHolder(false);
     if (source && source.isPlayer() !== target.isPlayer()) {
       applyAbAttrs(BlockItemTheftAbAttr, source, cancelled);
     }
-
     if (cancelled.value) {
       return false;
     }
 
-    const newItemModifier = itemModifier.clone() as PokemonHeldItemModifier;
+    // check if we have an item already and calc how much to transfer
-    newItemModifier.pokemonId = target.id;
     const matchingModifier = this.findModifier(
       m => m instanceof PokemonHeldItemModifier && m.matchType(itemModifier) && m.pokemonId === target.id,
       target.isPlayer(),
-    ) as PokemonHeldItemModifier;
+    ) as PokemonHeldItemModifier | undefined;
+    const countTaken = Math.min(
+      transferQuantity,
+      itemModifier.stackCount,
+      matchingModifier?.getCountUnderMax() ?? Number.MAX_SAFE_INTEGER,
+    );
+    if (countTaken <= 0) {
+      // Can't transfer negative items
+      return false;
+    }
 
+    itemModifier.stackCount -= countTaken;
+
+    // If the old modifier is at 0 stacks, try to remove it
+    if (itemModifier.stackCount <= 0 && !this.removeModifier(itemModifier, !source.isPlayer())) {
+      return false;
+    }
+
+    // TODO: what does this do and why is it here
+    if (source.isPlayer() !== target.isPlayer() && !ignoreUpdate) {
+      this.updateModifiers(source.isPlayer(), instant);
+    }
+
+    // Add however much we took to the recieving pokemon, creating a new modifier if the target lacked one prio
     if (matchingModifier) {
-      const maxStackCount = matchingModifier.getMaxStackCount();
+      matchingModifier.stackCount += countTaken;
-      if (matchingModifier.stackCount >= maxStackCount) {
-        return false;
-      }
-      const countTaken = Math.min(
-        transferQuantity,
-        itemModifier.stackCount,
-        maxStackCount - matchingModifier.stackCount,
-      );
-      itemModifier.stackCount -= countTaken;
-      newItemModifier.stackCount = matchingModifier.stackCount + countTaken;
     } else {
-      const countTaken = Math.min(transferQuantity, itemModifier.stackCount);
+      const newItemModifier = itemModifier.clone() as PokemonHeldItemModifier;
-      itemModifier.stackCount -= countTaken;
+      newItemModifier.pokemonId = target.id;
       newItemModifier.stackCount = countTaken;
-    }
+      if (target.isPlayer()) {
-
+        this.addModifier(newItemModifier, ignoreUpdate, playSound, false, instant);
-    const removeOld = itemModifier.stackCount === 0;
-
-    if (!removeOld || !source || this.removeModifier(itemModifier, !source.isPlayer())) {
-      const addModifier = () => {
-        if (!matchingModifier || this.removeModifier(matchingModifier, !target.isPlayer())) {
-          if (target.isPlayer()) {
-            this.addModifier(newItemModifier, ignoreUpdate, playSound, false, instant);
-            if (source && itemLost) {
-              applyPostItemLostAbAttrs(PostItemLostAbAttr, source, false);
-            }
-            return true;
-          }
-          this.addEnemyModifier(newItemModifier, ignoreUpdate, instant);
-          if (source && itemLost) {
-            applyPostItemLostAbAttrs(PostItemLostAbAttr, source, false);
-          }
-          return true;
-        }
-        return false;
-      };
-      if (source && source.isPlayer() !== target.isPlayer() && !ignoreUpdate) {
-        this.updateModifiers(source.isPlayer(), instant);
-        addModifier();
       } else {
-        addModifier();
+        this.addEnemyModifier(newItemModifier, ignoreUpdate, instant);
       }
-      return true;
     }
-    return false;
+
+    if (itemLost) {
+      applyPostItemLostAbAttrs(PostItemLostAbAttr, source, false);
+    }
+
+    return true;
   }
 
   canTransferHeldItemModifier(itemModifier: PokemonHeldItemModifier, target: Pokemon, transferQuantity = 1): boolean {
-    const mod = itemModifier.clone() as PokemonHeldItemModifier;
+    const source = itemModifier.getPokemon();
-    const source = mod.pokemonId ? mod.getPokemon() : null;
+    if (!source) {
-    const cancelled = new BooleanHolder(false);
+      console.error(
-
+        `Pokemon ${target.getNameToRender()} tried to transfer %d items from nonexistent source; item: `,
-    if (source && source.isPlayer() !== target.isPlayer()) {
+        transferQuantity,
-      applyAbAttrs(BlockItemTheftAbAttr, source, cancelled);
+        itemModifier,
+      );
+      return false;
     }
 
+    // Check theft prevention
+    // TODO: Verify whether sticky hold procs on friendly fire ally theft
+    const cancelled = new BooleanHolder(false);
+    if (source.isPlayer() !== target.isPlayer()) {
+      applyAbAttrs(BlockItemTheftAbAttr, source, cancelled);
+    }
     if (cancelled.value) {
       return false;
     }
 
+    // figure out if we can take anything
     const matchingModifier = this.findModifier(
-      m => m instanceof PokemonHeldItemModifier && m.matchType(mod) && m.pokemonId === target.id,
+      m => m instanceof PokemonHeldItemModifier && m.matchType(itemModifier) && m.pokemonId === target.id,
       target.isPlayer(),
-    ) as PokemonHeldItemModifier;
+    ) as PokemonHeldItemModifier | undefined;
-
+    const countTaken = Math.min(
-    if (matchingModifier) {
+      transferQuantity,
-      const maxStackCount = matchingModifier.getMaxStackCount();
+      itemModifier.stackCount,
-      if (matchingModifier.stackCount >= maxStackCount) {
+      matchingModifier?.getCountUnderMax() ?? Number.MAX_SAFE_INTEGER,
-        return false;
+    );
-      }
+    return countTaken > 0 && this.hasModifier(itemModifier, !source.isPlayer());
-      const countTaken = Math.min(transferQuantity, mod.stackCount, maxStackCount - matchingModifier.stackCount);
-      mod.stackCount -= countTaken;
-    } else {
-      const countTaken = Math.min(transferQuantity, mod.stackCount);
-      mod.stackCount -= countTaken;
-    }
-
-    const removeOld = mod.stackCount === 0;
-
-    return !removeOld || !source || this.hasModifier(itemModifier, !source.isPlayer());
   }
 
   removePartyMemberModifiers(partyMemberIndex: number): Promise<void> {
@@ -3286,6 +3296,7 @@ export default class BattleScene extends SceneBase {
       }
     }
 
+    // Why do we silently delete missing modifiers?
     const modifiersClone = modifiers.slice(0);
     for (const modifier of modifiersClone) {
       if (!modifier.getStackCount()) {
@@ -3311,44 +3322,71 @@ export default class BattleScene extends SceneBase {
     });
   }
 
+  /**
+   * Check whether a given {@linkcode PersistentModifier} exists on a given side of the field.
+   * @param modifier - The {@linkcode PersistentModifier} to check the existence of.
+   * @param enemy - Whether to check the enemy (`true`) or player (`false`) party. Default is `false`.
+   * @returns Whether the specified modifier exists on the given side of the field.
+   * @remarks This also compares `pokemonId`s to confirm a match (and therefore owners).
+   */
   hasModifier(modifier: PersistentModifier, enemy = false): boolean {
-    const modifiers = !enemy ? this.modifiers : this.enemyModifiers;
+    return (!enemy ? this.modifiers : this.enemyModifiers).includes(modifier);
-    return modifiers.indexOf(modifier) > -1;
   }
 
   /**
-   * Removes a currently owned item. If the item is stacked, the entire item stack
+   * Remove a currently owned item. If the item is stacked, the entire item stack
    * gets removed. This function does NOT apply in-battle effects, such as Unburden.
    * If in-battle effects are needed, use {@linkcode Pokemon.loseHeldItem} instead.
-   * @param modifier The item to be removed.
+   * @param modifier - The item to be removed.
-   * @param enemy `true` to remove an item owned by the enemy rather than the player; default `false`.
+   * @param enemy - Whether to remove from the enemy (`true`) or player (`false`) party; default `false`.
-   * @returns `true` if the item exists and was successfully removed, `false` otherwise
+   * @returns Whether the item exists and was successfully removed
    */
   removeModifier(modifier: PersistentModifier, enemy = false): boolean {
     const modifiers = !enemy ? this.modifiers : this.enemyModifiers;
     const modifierIndex = modifiers.indexOf(modifier);
-    if (modifierIndex > -1) {
+    if (modifierIndex === -1) {
-      modifiers.splice(modifierIndex, 1);
+      return false;
-      if (modifier instanceof PokemonFormChangeItemModifier) {
-        const pokemon = this.getPokemonById(modifier.pokemonId);
-        if (pokemon) {
-          modifier.apply(pokemon, false);
-        }
-      }
-      return true;
     }
 
-    return false;
+    modifiers.splice(modifierIndex, 1);
+    if (modifier instanceof PokemonFormChangeItemModifier) {
+      const pokemon = this.getPokemonById(modifier.pokemonId);
+      if (pokemon) {
+        modifier.apply(pokemon, false);
+      }
+    }
+    return true;
   }
 
   /**
-   * Get all of the modifiers that match `modifierType`
+   * Get all modifiers of all {@linkcode Pokemon} in the given party,
-   * @param modifierType The type of modifier to apply; must extend {@linkcode PersistentModifier}
+   * optionally filtering based on `modifierType` if provided.
-   * @param player Whether to search the player (`true`) or the enemy (`false`); Defaults to `true`
+   * @param player Whether to search the player (`true`) or enemy (`false`) party; Defaults to `true`
-   * @returns the list of all modifiers that matched `modifierType`.
+   * @returns An array containing all {@linkcode PersistentModifier}s on the given side of the field.
+   * @overload
    */
-  getModifiers<T extends PersistentModifier>(modifierType: Constructor<T>, player = true): T[] {
+  getModifiers(player?: boolean): PersistentModifier[];
-    return (player ? this.modifiers : this.enemyModifiers).filter((m): m is T => m instanceof modifierType);
+
+  /**
+   * Get all modifiers of all {@linkcode Pokemon} in the given party,
+   * optionally filtering based on `modifierType` if provided.
+   * @param modifierType The type of modifier to check against; must extend {@linkcode PersistentModifier}.
+   * If omitted, will return all {@linkcode PersistentModifier}s regardless of type.
+   * @param player Whether to search the player (`true`) or enemy (`false`) party; Defaults to `true`
+   * @returns An array containing all modifiers matching `modifierType` on the given side of the field.
+   * @overload
+   */
+  getModifiers<T extends PersistentModifier>(modifierType: Constructor<T>, player?: boolean): T[];
+
+  // NOTE: Boolean typing on 1st parameter needed to satisfy "bool only" overload
+  getModifiers<T extends PersistentModifier>(modifierType?: Constructor<T> | boolean, player?: boolean) {
+    const usePlayer: boolean = player ?? (typeof modifierType !== "boolean" || modifierType); // non-bool in 1st position = true by default
+    const mods = usePlayer ? this.modifiers : this.enemyModifiers;
+
+    if (typeof modifierType === "undefined" || typeof modifierType === "boolean") {
+      return mods;
+    }
+    return mods.filter((m): m is T => m instanceof modifierType);
   }
 
   /**

src/data/abilities/ability.ts

@@ -1246,7 +1246,7 @@ export class MoveTypeChangeAbAttr extends PreAttackAbAttr {
 
   /**
    * Determine if the move type change attribute can be applied
-   * 
+   *
    * Can be applied if:
    * - The ability's condition is met, e.g. pixilate only boosts normal moves,
    * - The move is not forbidden from having its type changed by an ability, e.g. {@linkcode Moves.MULTI_ATTACK}
@@ -1262,7 +1262,7 @@ export class MoveTypeChangeAbAttr extends PreAttackAbAttr {
    */
   override canApplyPreAttack(pokemon: Pokemon, _passive: boolean, _simulated: boolean, _defender: Pokemon | null, move: Move, _args: [NumberHolder?, NumberHolder?, ...any]): boolean {
     return (!this.condition || this.condition(pokemon, _defender, move)) &&
-            !noAbilityTypeOverrideMoves.has(move.id) && 
+            !noAbilityTypeOverrideMoves.has(move.id) &&
             (!pokemon.isTerastallized ||
               (move.id !== Moves.TERA_BLAST &&
               (move.id !== Moves.TERA_STARSTORM || pokemon.getTeraType() !== PokemonType.STELLAR || !pokemon.hasSpecies(Species.TERAPAGOS))));
@@ -1716,7 +1716,7 @@ export class GorillaTacticsAbAttr extends PostAttackAbAttr {
 
 export class PostAttackStealHeldItemAbAttr extends PostAttackAbAttr {
   private stealCondition: PokemonAttackCondition | null;
-  private stolenItem?: PokemonHeldItemModifier;
+  private stolenItem: PokemonHeldItemModifier;
 
   constructor(stealCondition?: PokemonAttackCondition) {
     super();
@@ -1731,39 +1731,37 @@ export class PostAttackStealHeldItemAbAttr extends PostAttackAbAttr {
     defender: Pokemon,
     move: Move,
     hitResult: HitResult,
-    args: any[]): boolean {
+    args: any[]
+  ): boolean {
+    // Check which items to steal
+    const heldItems = this.getTargetHeldItems(defender).filter((i) => i.isTransferable);
     if (
-      super.canApplyPostAttack(pokemon, passive, simulated, defender, move, hitResult, args) &&
+      !super.canApplyPostAttack(pokemon, passive, simulated, defender, move, hitResult, args) ||
-      !simulated &&
+      heldItems.length === 0 || // no items to steal
-      hitResult < HitResult.NO_EFFECT &&
+      hitResult >= HitResult.NO_EFFECT || // move was ineffective/protected against
-      (!this.stealCondition || this.stealCondition(pokemon, defender, move))
+      (this.stealCondition && !this.stealCondition(pokemon, defender, move)) // no condition = pass
     ) {
-      const heldItems = this.getTargetHeldItems(defender).filter((i) => i.isTransferable);
+      return false;
-      if (heldItems.length) {
-        // Ensure that the stolen item in testing is the same as when the effect is applied
-        this.stolenItem = heldItems[pokemon.randBattleSeedInt(heldItems.length)];
-        if (globalScene.canTransferHeldItemModifier(this.stolenItem, pokemon)) {
-          return true;
-        }
-      }
     }
-    this.stolenItem = undefined;
+
-    return false;
+    // pick random item and check if we can steal it
+    this.stolenItem = heldItems[pokemon.randBattleSeedInt(heldItems.length)];
+    return globalScene.canTransferHeldItemModifier(this.stolenItem, pokemon)
   }
 
   override applyPostAttack(
     pokemon: Pokemon,
-    passive: boolean,
+    _passive: boolean,
     simulated: boolean,
     defender: Pokemon,
-    move: Move,
+    _move: Move,
-    hitResult: HitResult,
+    _hitResult: HitResult,
-    args: any[],
+    _args: any[],
   ): void {
-    const heldItems = this.getTargetHeldItems(defender).filter((i) => i.isTransferable);
+    if (simulated) {
-    if (!this.stolenItem) {
+      return;
-      this.stolenItem = heldItems[pokemon.randBattleSeedInt(heldItems.length)];
     }
+
     if (globalScene.tryTransferHeldItemModifier(this.stolenItem, pokemon, false)) {
       globalScene.queueMessage(
         i18next.t("abilityTriggers:postAttackStealHeldItem", {
@@ -1773,7 +1771,6 @@ export class PostAttackStealHeldItemAbAttr extends PostAttackAbAttr {
         }),
       );
     }
-    this.stolenItem = undefined;
   }
 
   getTargetHeldItems(target: Pokemon): PokemonHeldItemModifier[] {
@@ -6629,7 +6626,8 @@ export function initAbilities() {
     new Ability(Abilities.STICKY_HOLD, 3)
       .attr(BlockItemTheftAbAttr)
       .bypassFaint()
-      .ignorable(),
+      .ignorable()
+      .edgeCase(), // may or may not proc incorrectly on user's allies
     new Ability(Abilities.SHED_SKIN, 3)
       .conditionalAttr(pokemon => !randSeedInt(3), PostTurnResetStatusAbAttr),
     new Ability(Abilities.GUTS, 3)

src/data/arena-tag.ts

@@ -87,10 +87,11 @@ export abstract class ArenaTag {
 
   /**
    * Helper function that retrieves the source Pokemon
-   * @returns The source {@linkcode Pokemon} or `null` if none is found
+   * @returns - The source {@linkcode Pokemon} for this tag.
+   * Returns `null` if `this.sourceId` is `undefined`
    */
   public getSourcePokemon(): Pokemon | null {
-    return this.sourceId ? globalScene.getPokemonById(this.sourceId) : null;
+    return globalScene.getPokemonById(this.sourceId);
   }
 
   /**
@@ -122,19 +123,22 @@ export class MistTag extends ArenaTag {
   onAdd(arena: Arena, quiet = false): void {
     super.onAdd(arena);
 
-    if (this.sourceId) {
+    // We assume `quiet=true` means "just add the bloody tag no questions asked"
-      const source = globalScene.getPokemonById(this.sourceId);
+    if (quiet) {
-
+      return;
-      if (!quiet && source) {
-        globalScene.queueMessage(
-          i18next.t("arenaTag:mistOnAdd", {
-            pokemonNameWithAffix: getPokemonNameWithAffix(source),
-          }),
-        );
-      } else if (!quiet) {
-        console.warn("Failed to get source for MistTag onAdd");
-      }
     }
+
+    const source = this.getSourcePokemon();
+    if (!source) {
+      console.warn(`Failed to get source Pokemon for MistTag on add message; id: ${this.sourceId}`);
+      return;
+    }
+
+    globalScene.queueMessage(
+      i18next.t("arenaTag:mistOnAdd", {
+        pokemonNameWithAffix: getPokemonNameWithAffix(source),
+      }),
+    );
   }
 
   /**
@@ -455,18 +459,18 @@ class MatBlockTag extends ConditionalProtectTag {
   }
 
   onAdd(_arena: Arena) {
-    if (this.sourceId) {
+    const source = this.getSourcePokemon();
-      const source = globalScene.getPokemonById(this.sourceId);
+    if (!source) {
-      if (source) {
+      console.warn(`Failed to get source Pokemon for Mat Block message; id: ${this.sourceId}`);
-        globalScene.queueMessage(
+      return;
-          i18next.t("arenaTag:matBlockOnAdd", {
-            pokemonNameWithAffix: getPokemonNameWithAffix(source),
-          }),
-        );
-      } else {
-        console.warn("Failed to get source for MatBlockTag onAdd");
-      }
     }
+
+    super.onAdd(_arena);
+    globalScene.queueMessage(
+      i18next.t("arenaTag:matBlockOnAdd", {
+        pokemonNameWithAffix: getPokemonNameWithAffix(source),
+      }),
+    );
   }
 }
 
@@ -526,7 +530,12 @@ export class NoCritTag extends ArenaTag {
 
   /** Queues a message upon removing this effect from the field */
   onRemove(_arena: Arena): void {
-    const source = globalScene.getPokemonById(this.sourceId!); // TODO: is this bang correct?
+    const source = this.getSourcePokemon();
+    if (!source) {
+      console.warn(`Failed to get source Pokemon for NoCritTag on remove message; id: ${this.sourceId}`);
+      return;
+    }
+
     globalScene.queueMessage(
       i18next.t("arenaTag:noCritOnRemove", {
         pokemonNameWithAffix: getPokemonNameWithAffix(source ?? undefined),
@@ -537,7 +546,7 @@ export class NoCritTag extends ArenaTag {
 }
 
 /**
- * Arena Tag class for {@link https://bulbapedia.bulbagarden.net/wiki/Wish_(move) Wish}.
+ * Arena Tag class for {@link https://bulbapedia.bulbagarden.net/wiki/Wish_(move) | Wish}.
  * Heals the Pokémon in the user's position the turn after Wish is used.
  */
 class WishTag extends ArenaTag {
@@ -550,18 +559,20 @@ class WishTag extends ArenaTag {
   }
 
   onAdd(_arena: Arena): void {
-    if (this.sourceId) {
+    const source = this.getSourcePokemon();
-      const user = globalScene.getPokemonById(this.sourceId);
+    if (!source) {
-      if (user) {
+      console.warn(`Failed to get source Pokemon for WishTag on add message; id: ${this.sourceId}`);
-        this.battlerIndex = user.getBattlerIndex();
+      return;
-        this.triggerMessage = i18next.t("arenaTag:wishTagOnAdd", {
-          pokemonNameWithAffix: getPokemonNameWithAffix(user),
-        });
-        this.healHp = toDmgValue(user.getMaxHp() / 2);
-      } else {
-        console.warn("Failed to get source for WishTag onAdd");
-      }
     }
+
+    super.onAdd(_arena);
+    this.healHp = toDmgValue(source.getMaxHp() / 2);
+
+    globalScene.queueMessage(
+      i18next.t("arenaTag:wishTagOnAdd", {
+        pokemonNameWithAffix: getPokemonNameWithAffix(source),
+      }),
+    );
   }
 
   onRemove(_arena: Arena): void {
@@ -756,15 +767,23 @@ class SpikesTag extends ArenaTrapTag {
   onAdd(arena: Arena, quiet = false): void {
     super.onAdd(arena);
 
-    const source = this.sourceId ? globalScene.getPokemonById(this.sourceId) : null;
+    // We assume `quiet=true` means "just add the bloody tag no questions asked"
-    if (!quiet && source) {
+    if (quiet) {
-      globalScene.queueMessage(
+      return;
-        i18next.t("arenaTag:spikesOnAdd", {
-          moveName: this.getMoveName(),
-          opponentDesc: source.getOpponentDescriptor(),
-        }),
-      );
     }
+
+    const source = this.getSourcePokemon();
+    if (!source) {
+      console.warn(`Failed to get source Pokemon for SpikesTag on add message; id: ${this.sourceId}`);
+      return;
+    }
+
+    globalScene.queueMessage(
+      i18next.t("arenaTag:spikesOnAdd", {
+        moveName: this.getMoveName(),
+        opponentDesc: source.getOpponentDescriptor(),
+      }),
+    );
   }
 
   override activateTrap(pokemon: Pokemon, simulated: boolean): boolean {
@@ -809,15 +828,23 @@ class ToxicSpikesTag extends ArenaTrapTag {
   onAdd(arena: Arena, quiet = false): void {
     super.onAdd(arena);
 
-    const source = this.sourceId ? globalScene.getPokemonById(this.sourceId) : null;
+    if (quiet) {
-    if (!quiet && source) {
+      // We assume `quiet=true` means "just add the bloody tag no questions asked"
-      globalScene.queueMessage(
+      return;
-        i18next.t("arenaTag:toxicSpikesOnAdd", {
-          moveName: this.getMoveName(),
-          opponentDesc: source.getOpponentDescriptor(),
-        }),
-      );
     }
+
+    const source = this.getSourcePokemon();
+    if (!source) {
+      console.warn(`Failed to get source Pokemon for ToxicSpikesTag on add message; id: ${this.sourceId}`);
+      return;
+    }
+
+    globalScene.queueMessage(
+      i18next.t("arenaTag:toxicSpikesOnAdd", {
+        moveName: this.getMoveName(),
+        opponentDesc: source.getOpponentDescriptor(),
+      }),
+    );
   }
 
   onRemove(arena: Arena): void {
@@ -915,7 +942,11 @@ class StealthRockTag extends ArenaTrapTag {
   onAdd(arena: Arena, quiet = false): void {
     super.onAdd(arena);
 
-    const source = this.sourceId ? globalScene.getPokemonById(this.sourceId) : null;
+    if (quiet) {
+      return;
+    }
+
+    const source = this.getSourcePokemon();
     if (!quiet && source) {
       globalScene.queueMessage(
         i18next.t("arenaTag:stealthRockOnAdd", {
@@ -999,15 +1030,24 @@ class StickyWebTag extends ArenaTrapTag {
 
   onAdd(arena: Arena, quiet = false): void {
     super.onAdd(arena);
-    const source = this.sourceId ? globalScene.getPokemonById(this.sourceId) : null;
+
-    if (!quiet && source) {
+    // We assume `quiet=true` means "just add the bloody tag no questions asked"
-      globalScene.queueMessage(
+    if (quiet) {
-        i18next.t("arenaTag:stickyWebOnAdd", {
+      return;
-          moveName: this.getMoveName(),
-          opponentDesc: source.getOpponentDescriptor(),
-        }),
-      );
     }
+
+    const source = this.getSourcePokemon();
+    if (!source) {
+      console.warn(`Failed to get source Pokemon for SpikesTag on add message; id: ${this.sourceId}`);
+      return;
+    }
+
+    globalScene.queueMessage(
+      i18next.t("arenaTag:spikesOnAdd", {
+        moveName: this.getMoveName(),
+        opponentDesc: source.getOpponentDescriptor(),
+      }),
+    );
   }
 
   override activateTrap(pokemon: Pokemon, simulated: boolean): boolean {
@@ -1072,14 +1112,20 @@ export class TrickRoomTag extends ArenaTag {
   }
 
   onAdd(_arena: Arena): void {
-    const source = this.sourceId ? globalScene.getPokemonById(this.sourceId) : null;
+    super.onAdd(_arena);
-    if (source) {
+
-      globalScene.queueMessage(
+    const source = this.getSourcePokemon();
-        i18next.t("arenaTag:trickRoomOnAdd", {
+    if (!source) {
-          pokemonNameWithAffix: getPokemonNameWithAffix(source),
+      console.warn(`Failed to get source Pokemon for TrickRoomTag on add message; id: ${this.sourceId}`);
-        }),
+      return;
-      );
     }
+
+    globalScene.queueMessage(
+      i18next.t("arenaTag:spikesOnAdd", {
+        moveName: this.getMoveName(),
+        opponentDesc: source.getOpponentDescriptor(),
+      }),
+    );
   }
 
   onRemove(_arena: Arena): void {
@@ -1126,6 +1172,13 @@ class TailwindTag extends ArenaTag {
   }
 
   onAdd(_arena: Arena, quiet = false): void {
+    const source = this.getSourcePokemon();
+    if (!source) {
+      return;
+    }
+
+    super.onAdd(_arena, quiet);
+
     if (!quiet) {
       globalScene.queueMessage(
         i18next.t(
@@ -1134,10 +1187,9 @@ class TailwindTag extends ArenaTag {
       );
     }
 
-    const source = globalScene.getPokemonById(this.sourceId!); //TODO: this bang is questionable!
+    const field = source.isPlayer() ? globalScene.getPlayerField() : globalScene.getEnemyField();
-    const party = (source?.isPlayer() ? globalScene.getPlayerField() : globalScene.getEnemyField()) ?? [];
 
-    for (const pokemon of party) {
+    for (const pokemon of field) {
       // Apply the CHARGED tag to party members with the WIND_POWER ability
       if (pokemon.hasAbility(Abilities.WIND_POWER) && !pokemon.getTag(BattlerTagType.CHARGED)) {
         pokemon.addTag(BattlerTagType.CHARGED);
@@ -1225,24 +1277,25 @@ class ImprisonTag extends ArenaTrapTag {
   }
 
   /**
-   * This function applies the effects of Imprison to the opposing Pokemon already present on the field.
+   * Apply the effects of Imprison to all opposing on-field Pokemon.
-   * @param arena
    */
   override onAdd() {
     const source = this.getSourcePokemon();
-    if (source) {
+    if (!source) {
-      const party = this.getAffectedPokemon();
+      return;
-      party?.forEach((p: Pokemon) => {
-        if (p.isAllowedInBattle()) {
-          p.addTag(BattlerTagType.IMPRISON, 1, Moves.IMPRISON, this.sourceId);
-        }
-      });
-      globalScene.queueMessage(
-        i18next.t("battlerTags:imprisonOnAdd", {
-          pokemonNameWithAffix: getPokemonNameWithAffix(source),
-        }),
-      );
     }
+
+    const party = this.getAffectedPokemon();
+    party.forEach((p: Pokemon) => {
+      if (p.isAllowedInBattle()) {
+        p.addTag(BattlerTagType.IMPRISON, 1, Moves.IMPRISON, this.sourceId);
+      }
+    });
+    globalScene.queueMessage(
+      i18next.t("battlerTags:imprisonOnAdd", {
+        pokemonNameWithAffix: getPokemonNameWithAffix(source),
+      }),
+    );
   }
 
   /**

src/data/battler-tags.ts

@@ -129,7 +129,7 @@ export class BattlerTag {
    * @returns The source {@linkcode Pokemon}, or `null` if none is found
    */
   public getSourcePokemon(): Pokemon | null {
-    return this.sourceId ? globalScene.getPokemonById(this.sourceId) : null;
+    return globalScene.getPokemonById(this.sourceId);
   }
 }
 
@@ -585,9 +585,13 @@ export class TrappedTag extends BattlerTag {
   }
 
   canAdd(pokemon: Pokemon): boolean {
-    const source = globalScene.getPokemonById(this.sourceId!)!;
+    const source = this.getSourcePokemon();
-    const move = allMoves[this.sourceMove];
+    if (!source) {
+      console.warn(`Failed to get source Pokemon for TrappedTag canAdd; id: ${this.sourceId}`);
+      return false;
+    }
 
+    const move = allMoves[this.sourceMove];
     const isGhost = pokemon.isOfType(PokemonType.GHOST);
     const isTrapped = pokemon.getTag(TrappedTag);
     const hasSubstitute = move.hitsSubstitute(source, pokemon);
@@ -809,12 +813,20 @@ export class DestinyBondTag extends BattlerTag {
     if (lapseType !== BattlerTagLapseType.CUSTOM) {
       return super.lapse(pokemon, lapseType);
     }
-    const source = this.sourceId ? globalScene.getPokemonById(this.sourceId) : null;
+
-    if (!source?.isFainted()) {
+    const source = this.getSourcePokemon();
+    if (!source) {
+      console.warn(`Failed to get source Pokemon for DestinyBondTag lapse; id: ${this.sourceId}`);
+      return false;
+    }
+
+    // Destiny bond stays active until the user faints
+    if (!source.isFainted()) {
       return true;
     }
 
-    if (source?.getAlly() === pokemon) {
+    // Don't kill allies
+    if (source.getAlly() === pokemon) {
       return false;
     }
 
@@ -827,6 +839,7 @@ export class DestinyBondTag extends BattlerTag {
       return false;
     }
 
+    // Drag the foe down with the user
     globalScene.queueMessage(
       i18next.t("battlerTags:destinyBondLapse", {
         pokemonNameWithAffix: getPokemonNameWithAffix(source),
@@ -844,17 +857,13 @@ export class InfatuatedTag extends BattlerTag {
   }
 
   canAdd(pokemon: Pokemon): boolean {
-    if (this.sourceId) {
+    const source = this.getSourcePokemon();
-      const pkm = globalScene.getPokemonById(this.sourceId);
+    if (!source) {
-
+      console.warn(`Failed to get source Pokemon for InfatuatedTag canAdd; id: ${this.sourceId}`);
-      if (pkm) {
-        return pokemon.isOppositeGender(pkm);
-      }
-      console.warn("canAdd: this.sourceId is not a valid pokemon id!", this.sourceId);
       return false;
     }
-    console.warn("canAdd: this.sourceId is undefined");
+
-    return false;
+    return pokemon.isOppositeGender(source);
   }
 
   onAdd(pokemon: Pokemon): void {
@@ -863,7 +872,7 @@ export class InfatuatedTag extends BattlerTag {
     globalScene.queueMessage(
       i18next.t("battlerTags:infatuatedOnAdd", {
         pokemonNameWithAffix: getPokemonNameWithAffix(pokemon),
-        sourcePokemonName: getPokemonNameWithAffix(globalScene.getPokemonById(this.sourceId!) ?? undefined), // TODO: is that bang correct?
+        sourcePokemonName: getPokemonNameWithAffix(this.getSourcePokemon()!), // Tag not added + console warns if no source
       }),
     );
   }
@@ -881,26 +890,35 @@ export class InfatuatedTag extends BattlerTag {
   lapse(pokemon: Pokemon, lapseType: BattlerTagLapseType): boolean {
     const ret = lapseType !== BattlerTagLapseType.CUSTOM || super.lapse(pokemon, lapseType);
 
-    if (ret) {
+    if (!ret) {
-      globalScene.queueMessage(
+      return false;
-        i18next.t("battlerTags:infatuatedLapse", {
-          pokemonNameWithAffix: getPokemonNameWithAffix(pokemon),
-          sourcePokemonName: getPokemonNameWithAffix(globalScene.getPokemonById(this.sourceId!) ?? undefined), // TODO: is that bang correct?
-        }),
-      );
-      globalScene.unshiftPhase(new CommonAnimPhase(pokemon.getBattlerIndex(), undefined, CommonAnim.ATTRACT));
-
-      if (pokemon.randBattleSeedInt(2)) {
-        globalScene.queueMessage(
-          i18next.t("battlerTags:infatuatedLapseImmobilize", {
-            pokemonNameWithAffix: getPokemonNameWithAffix(pokemon),
-          }),
-        );
-        (globalScene.getCurrentPhase() as MovePhase).cancel();
-      }
     }
 
-    return ret;
+    const source = this.getSourcePokemon();
+    if (!source) {
+      console.warn(`Failed to get source Pokemon for InfatuatedTag lapse; id: ${this.sourceId}`);
+      return false;
+    }
+
+    globalScene.queueMessage(
+      i18next.t("battlerTags:infatuatedLapse", {
+        pokemonNameWithAffix: getPokemonNameWithAffix(pokemon),
+        sourcePokemonName: getPokemonNameWithAffix(source),
+      }),
+    );
+    globalScene.unshiftPhase(new CommonAnimPhase(pokemon.getBattlerIndex(), undefined, CommonAnim.ATTRACT));
+
+    // 50% chance to disrupt the target's action
+    if (pokemon.randBattleSeedInt(2) === 0) {
+      globalScene.queueMessage(
+        i18next.t("battlerTags:infatuatedLapseImmobilize", {
+          pokemonNameWithAffix: getPokemonNameWithAffix(pokemon),
+        }),
+      );
+      (globalScene.getCurrentPhase() as MovePhase).cancel();
+    }
+
+    return true;
   }
 
   onRemove(pokemon: Pokemon): void {
@@ -943,6 +961,12 @@ export class SeedTag extends BattlerTag {
   }
 
   onAdd(pokemon: Pokemon): void {
+    const source = this.getSourcePokemon();
+    if (!source) {
+      console.warn(`Failed to get source Pokemon for SeedTag onAdd; id: ${this.sourceId}`);
+      return;
+    }
+
     super.onAdd(pokemon);
 
     globalScene.queueMessage(
@@ -950,45 +974,52 @@ export class SeedTag extends BattlerTag {
         pokemonNameWithAffix: getPokemonNameWithAffix(pokemon),
       }),
     );
-    this.sourceIndex = globalScene.getPokemonById(this.sourceId!)!.getBattlerIndex(); // TODO: are those bangs correct?
+    this.sourceIndex = source.getBattlerIndex();
   }
 
   lapse(pokemon: Pokemon, lapseType: BattlerTagLapseType): boolean {
     const ret = lapseType !== BattlerTagLapseType.CUSTOM || super.lapse(pokemon, lapseType);
 
-    if (ret) {
+    if (!ret) {
-      const source = pokemon.getOpponents().find(o => o.getBattlerIndex() === this.sourceIndex);
+      return false;
-      if (source) {
-        const cancelled = new BooleanHolder(false);
-        applyAbAttrs(BlockNonDirectDamageAbAttr, pokemon, cancelled);
-
-        if (!cancelled.value) {
-          globalScene.unshiftPhase(
-            new CommonAnimPhase(source.getBattlerIndex(), pokemon.getBattlerIndex(), CommonAnim.LEECH_SEED),
-          );
-
-          const damage = pokemon.damageAndUpdate(toDmgValue(pokemon.getMaxHp() / 8), { result: HitResult.INDIRECT });
-          const reverseDrain = pokemon.hasAbilityWithAttr(ReverseDrainAbAttr, false);
-          globalScene.unshiftPhase(
-            new PokemonHealPhase(
-              source.getBattlerIndex(),
-              !reverseDrain ? damage : damage * -1,
-              !reverseDrain
-                ? i18next.t("battlerTags:seededLapse", {
-                    pokemonNameWithAffix: getPokemonNameWithAffix(pokemon),
-                  })
-                : i18next.t("battlerTags:seededLapseShed", {
-                    pokemonNameWithAffix: getPokemonNameWithAffix(pokemon),
-                  }),
-              false,
-              true,
-            ),
-          );
-        }
-      }
     }
 
-    return ret;
+    // Check which opponent to restore HP to
+    const source = pokemon.getOpponents().find(o => o.getBattlerIndex() === this.sourceIndex);
+    if (!source) {
+      console.warn(`Failed to get source Pokemon for SeedTag lapse; id: ${this.sourceId}`);
+      return false;
+    }
+
+    const cancelled = new BooleanHolder(false);
+    applyAbAttrs(BlockNonDirectDamageAbAttr, pokemon, cancelled);
+
+    if (cancelled.value) {
+      return true;
+    }
+
+    globalScene.unshiftPhase(
+      new CommonAnimPhase(source.getBattlerIndex(), pokemon.getBattlerIndex(), CommonAnim.LEECH_SEED),
+    );
+
+    const damage = pokemon.damageAndUpdate(toDmgValue(pokemon.getMaxHp() / 8), { result: HitResult.INDIRECT });
+    const reverseDrain = pokemon.hasAbilityWithAttr(ReverseDrainAbAttr, false);
+    globalScene.unshiftPhase(
+      new PokemonHealPhase(
+        source.getBattlerIndex(),
+        !reverseDrain ? damage : damage * -1,
+        !reverseDrain
+          ? i18next.t("battlerTags:seededLapse", {
+              pokemonNameWithAffix: getPokemonNameWithAffix(pokemon),
+            })
+          : i18next.t("battlerTags:seededLapseShed", {
+              pokemonNameWithAffix: getPokemonNameWithAffix(pokemon),
+            }),
+        false,
+        true,
+      ),
+    );
+    return true;
   }
 
   getDescriptor(): string {
@@ -1245,9 +1276,15 @@ export class HelpingHandTag extends BattlerTag {
   }
 
   onAdd(pokemon: Pokemon): void {
+    const source = this.getSourcePokemon();
+    if (!source) {
+      console.warn(`Failed to get source Pokemon for HelpingHandTag onAdd; id: ${this.sourceId}`);
+      return;
+    }
+
     globalScene.queueMessage(
       i18next.t("battlerTags:helpingHandOnAdd", {
-        pokemonNameWithAffix: getPokemonNameWithAffix(globalScene.getPokemonById(this.sourceId!) ?? undefined), // TODO: is that bang correct?
+        pokemonNameWithAffix: getPokemonNameWithAffix(source),
         pokemonName: getPokemonNameWithAffix(pokemon),
       }),
     );
@@ -1459,15 +1496,22 @@ export abstract class DamagingTrapTag extends TrappedTag {
   }
 }
 
+// TODO: Condense all these tags into 1 singular tag with a modified message func
 export class BindTag extends DamagingTrapTag {
   constructor(turnCount: number, sourceId: number) {
     super(BattlerTagType.BIND, CommonAnim.BIND, turnCount, Moves.BIND, sourceId);
   }
 
   getTrapMessage(pokemon: Pokemon): string {
+    const source = this.getSourcePokemon();
+    if (!source) {
+      console.warn(`Failed to get source Pokemon for BindTag getTrapMessage; id: ${this.sourceId}`);
+      return "ERROR - CHECK CONSOLE AND REPORT";
+    }
+
     return i18next.t("battlerTags:bindOnTrap", {
       pokemonNameWithAffix: getPokemonNameWithAffix(pokemon),
-      sourcePokemonName: getPokemonNameWithAffix(globalScene.getPokemonById(this.sourceId!) ?? undefined), // TODO: is that bang correct?
+      sourcePokemonName: getPokemonNameWithAffix(source),
       moveName: this.getMoveName(),
     });
   }
@@ -1479,9 +1523,16 @@ export class WrapTag extends DamagingTrapTag {
   }
 
   getTrapMessage(pokemon: Pokemon): string {
-    return i18next.t("battlerTags:wrapOnTrap", {
+    const source = this.getSourcePokemon();
+    if (!source) {
+      console.warn(`Failed to get source Pokemon for ClampTag getTrapMessage; id: ${this.sourceId}`);
+      return "ERROR - CHECK CONSOLE AND REPORT";
+    }
+
+    return i18next.t("battlerTags:clampOnTrap", {
       pokemonNameWithAffix: getPokemonNameWithAffix(pokemon),
-      sourcePokemonName: getPokemonNameWithAffix(globalScene.getPokemonById(this.sourceId!) ?? undefined), // TODO: is that bang correct?
+      sourcePokemonName: getPokemonNameWithAffix(source),
+      moveName: this.getMoveName(),
     });
   }
 }
@@ -1516,8 +1567,14 @@ export class ClampTag extends DamagingTrapTag {
   }
 
   getTrapMessage(pokemon: Pokemon): string {
+    const source = this.getSourcePokemon();
+    if (!source) {
+      console.warn(`Failed to get source Pokemon for ClampTag getTrapMessage; id: ${this.sourceId}`);
+      return "ERROR - CHECK CONSOLE AND REPORT ASAP";
+    }
+
     return i18next.t("battlerTags:clampOnTrap", {
-      sourcePokemonNameWithAffix: getPokemonNameWithAffix(globalScene.getPokemonById(this.sourceId!) ?? undefined), // TODO: is that bang correct?
+      sourcePokemonNameWithAffix: getPokemonNameWithAffix(source),
       pokemonName: getPokemonNameWithAffix(pokemon),
     });
   }
@@ -1566,9 +1623,15 @@ export class ThunderCageTag extends DamagingTrapTag {
   }
 
   getTrapMessage(pokemon: Pokemon): string {
+    const source = this.getSourcePokemon();
+    if (!source) {
+      console.warn(`Failed to get source Pokemon for ThunderCageTag getTrapMessage; id: ${this.sourceId}`);
+      return "ERROR - PLEASE REPORT ASAP";
+    }
+
     return i18next.t("battlerTags:thunderCageOnTrap", {
       pokemonNameWithAffix: getPokemonNameWithAffix(pokemon),
-      sourcePokemonNameWithAffix: getPokemonNameWithAffix(globalScene.getPokemonById(this.sourceId!) ?? undefined), // TODO: is that bang correct?
+      sourcePokemonNameWithAffix: getPokemonNameWithAffix(source),
     });
   }
 }
@@ -1579,9 +1642,15 @@ export class InfestationTag extends DamagingTrapTag {
   }
 
   getTrapMessage(pokemon: Pokemon): string {
+    const source = this.getSourcePokemon();
+    if (!source) {
+      console.warn(`Failed to get source Pokemon for InfestationTag getTrapMessage; id: ${this.sourceId}`);
+      return "ERROR - CHECK CONSOLE AND REPORT";
+    }
+
     return i18next.t("battlerTags:infestationOnTrap", {
       pokemonNameWithAffix: getPokemonNameWithAffix(pokemon),
-      sourcePokemonNameWithAffix: getPokemonNameWithAffix(globalScene.getPokemonById(this.sourceId!) ?? undefined), // TODO: is that bang correct?
+      sourcePokemonNameWithAffix: getPokemonNameWithAffix(source),
     });
   }
 }
@@ -2253,14 +2322,19 @@ export class SaltCuredTag extends BattlerTag {
   }
 
   onAdd(pokemon: Pokemon): void {
-    super.onAdd(pokemon);
+    const source = this.getSourcePokemon();
+    if (!source) {
+      console.warn(`Failed to get source Pokemon for SaltCureTag onAdd; id: ${this.sourceId}`);
+      return;
+    }
 
+    super.onAdd(pokemon);
     globalScene.queueMessage(
       i18next.t("battlerTags:saltCuredOnAdd", {
         pokemonNameWithAffix: getPokemonNameWithAffix(pokemon),
       }),
     );
-    this.sourceIndex = globalScene.getPokemonById(this.sourceId!)!.getBattlerIndex(); // TODO: are those bangs correct?
+    this.sourceIndex = source.getBattlerIndex();
   }
 
   lapse(pokemon: Pokemon, lapseType: BattlerTagLapseType): boolean {
@@ -2310,8 +2384,14 @@ export class CursedTag extends BattlerTag {
   }
 
   onAdd(pokemon: Pokemon): void {
+    const source = this.getSourcePokemon();
+    if (!source) {
+      console.warn(`Failed to get source Pokemon for CursedTag onAdd; id: ${this.sourceId}`);
+      return;
+    }
+
     super.onAdd(pokemon);
-    this.sourceIndex = globalScene.getPokemonById(this.sourceId!)!.getBattlerIndex(); // TODO: are those bangs correct?
+    this.sourceIndex = source.getBattlerIndex();
   }
 
   lapse(pokemon: Pokemon, lapseType: BattlerTagLapseType): boolean {
@@ -2922,7 +3002,13 @@ export class SubstituteTag extends BattlerTag {
 
   /** Sets the Substitute's HP and queues an on-add battle animation that initializes the Substitute's sprite. */
   onAdd(pokemon: Pokemon): void {
-    this.hp = Math.floor(globalScene.getPokemonById(this.sourceId!)!.getMaxHp() / 4);
+    const source = this.getSourcePokemon();
+    if (!source) {
+      console.warn(`Failed to get source Pokemon for SubstituteTag onAdd; id: ${this.sourceId}`);
+      return;
+    }
+
+    this.hp = Math.floor(source.getMaxHp() / 4);
     this.sourceInFocus = false;
 
     // Queue battle animation and message
@@ -3205,13 +3291,14 @@ export class ImprisonTag extends MoveRestrictionBattlerTag {
    */
   public override lapse(pokemon: Pokemon, lapseType: BattlerTagLapseType): boolean {
     const source = this.getSourcePokemon();
-    if (source) {
+    if (!source) {
-      if (lapseType === BattlerTagLapseType.PRE_MOVE) {
+      console.warn(`Failed to get source Pokemon for ImprisonTag lapse; id: ${this.sourceId}`);
-        return super.lapse(pokemon, lapseType) && source.isActive(true);
+      return false;
-      }
-      return source.isActive(true);
     }
-    return false;
+    if (lapseType === BattlerTagLapseType.PRE_MOVE) {
+      return super.lapse(pokemon, lapseType) && source.isActive(true);
+    }
+    return source.isActive(true);
   }
 
   /**
@@ -3271,12 +3358,20 @@ export class SyrupBombTag extends BattlerTag {
    * Applies the single-stage speed down to the target Pokemon and decrements the tag's turn count
    * @param pokemon - The target {@linkcode Pokemon}
    * @param _lapseType - N/A
-   * @returns `true` if the `turnCount` is still greater than `0`; `false` if the `turnCount` is `0` or the target or source Pokemon has been removed from the field
+   * @returns Whether the tag should persist (`turnsRemaining > 0` and source still on field)
    */
   override lapse(pokemon: Pokemon, _lapseType: BattlerTagLapseType): boolean {
-    if (this.sourceId && !globalScene.getPokemonById(this.sourceId)?.isActive(true)) {
+    const source = this.getSourcePokemon();
+    if (!source) {
+      console.warn(`Failed to get source Pokemon for SyrupBombTag lapse; id: ${this.sourceId}`);
       return false;
     }
+
+    // Syrup bomb clears immediately if source leaves field/faints
+    if (!source.isActive(true)) {
+      return false;
+    }
+
     // Custom message in lieu of an animation in mainline
     globalScene.queueMessage(
       i18next.t("battlerTags:syrupBombLapse", {
@@ -3286,7 +3381,7 @@ export class SyrupBombTag extends BattlerTag {
     globalScene.unshiftPhase(
       new StatStageChangePhase(pokemon.getBattlerIndex(), true, [Stat.SPD], -1, true, false, true),
     );
-    return --this.turnCount > 0;
+    return super.lapse(pokemon, _lapseType);
   }
 }
 

src/data/moves/move.ts

@@ -6822,17 +6822,17 @@ export class RandomMovesetMoveAttr extends CallMoveAttr {
       // includeParty will be true for Assist, false for Sleep Talk
       let allies: Pokemon[];
       if (this.includeParty) {
-        allies = user.isPlayer() ? globalScene.getPlayerParty().filter(p => p !== user) : globalScene.getEnemyParty().filter(p => p !== user);
+        allies = (user.isPlayer() ? globalScene.getPlayerParty() : globalScene.getEnemyParty()).filter(p => p !== user);
       } else {
         allies = [ user ];
       }
-      const partyMoveset = allies.map(p => p.moveset).flat();
+      const partyMoveset = allies.flatMap(p => p.moveset);
-      const moves = partyMoveset.filter(m => !this.invalidMoves.has(m!.moveId) && !m!.getMove().name.endsWith(" (N)"));
+      const moves = partyMoveset.filter(m => !this.invalidMoves.has(m.moveId) && !m.getMove().name.endsWith(" (N)"));
       if (moves.length === 0) {
         return false;
       }
 
-      this.moveId = moves[user.randBattleSeedInt(moves.length)]!.moveId;
+      this.moveId = moves[user.randBattleSeedInt(moves.length)].moveId;
       return true;
     };
   }

src/data/mystery-encounters/encounters/dancing-lessons-encounter.ts

@@ -327,7 +327,7 @@ export const DancingLessonsEncounter: MysteryEncounter = MysteryEncounterBuilder
       .withOptionPhase(async () => {
         // Show the Oricorio a dance, and recruit it
         const encounter = globalScene.currentBattle.mysteryEncounter!;
-        const oricorio = encounter.misc.oricorioData.toPokemon();
+        const oricorio = encounter.misc.oricorioData.toPokemon() as EnemyPokemon;
         oricorio.passive = true;
 
         // Ensure the Oricorio's moveset gains the Dance move the player used

src/field/pokemon.ts

@@ -311,6 +311,7 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
    * TODO: Stop treating this like a unique ID and stop treating 0 as no pokemon
    */
   public id: number;
+  public pid: number;
   public name: string;
   public nickname: string;
   public species: PokemonSpecies;
@@ -4172,7 +4173,7 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
   getTag<T extends BattlerTag>(tagType: Constructor<T>): T | undefined;
 
   getTag(tagType: BattlerTagType | Constructor<BattlerTag>): BattlerTag | undefined {
-    return tagType instanceof Function
+    return typeof tagType === "function"
       ? this.summonData.tags.find(t => t instanceof tagType)
       : this.summonData.tags.find(t => t.tagType === tagType);
   }
@@ -6702,7 +6703,7 @@ export class EnemyPokemon extends Pokemon {
     return ret;
   }
 
-  
+
   /**
    * Show or hide the type effectiveness multiplier window
    * Passing undefined will hide the window

src/modifier/modifier.ts

@@ -738,7 +738,7 @@ export abstract class PokemonHeldItemModifier extends PersistentModifier {
   }
 
   getPokemon(): Pokemon | undefined {
-    return this.pokemonId ? (globalScene.getPokemonById(this.pokemonId) ?? undefined) : undefined;
+    return globalScene.getPokemonById(this.pokemonId) ?? undefined;
   }
 
   getScoreMultiplier(): number {

test/abilities/unburden.test.ts

@@ -23,10 +23,7 @@ describe("Abilities - Unburden", () => {
    */
   function getHeldItemCount(pokemon: Pokemon): number {
     const stackCounts = pokemon.getHeldItems().map(m => m.getStackCount());
-    if (stackCounts.length) {
+    return stackCounts.reduce((a, b) => a + b, 0);
-      return stackCounts.reduce((a, b) => a + b);
-    }
-    return 0;
   }
 
   beforeAll(() => {
@@ -318,7 +315,7 @@ describe("Abilities - Unburden", () => {
   });
 
   it("should activate when a reviver seed is used", async () => {
-    game.override.startingHeldItems([{ name: "REVIVER_SEED" }]).enemyMoveset([Moves.WING_ATTACK]);
+    game.override.startingHeldItems([{ name: "REVIVER_SEED" }]).enemyMoveset(Moves.WING_ATTACK);
     await game.classicMode.startBattle([Species.TREECKO]);
 
     const playerPokemon = game.scene.getPlayerPokemon()!;

test/field/pokemon_id_checks.test.ts

@@ -0,0 +1,104 @@
+import { allMoves } from "#app/data/moves/move";
+import type Pokemon from "#app/field/pokemon";
+import { BerryModifier } from "#app/modifier/modifier";
+import { Abilities } from "#enums/abilities";
+import { BattleType } from "#enums/battle-type";
+import { BattlerTagType } from "#enums/battler-tag-type";
+import { BerryType } from "#enums/berry-type";
+import { Moves } from "#enums/moves";
+import { Species } from "#enums/species";
+import { Stat } from "#enums/stat";
+import GameManager from "#test/testUtils/gameManager";
+import Phaser from "phaser";
+import { afterEach, beforeAll, beforeEach, describe, expect, it, vi } from "vitest";
+
+describe("Field - Pokemon ID Checks", () => {
+  let phaserGame: Phaser.Game;
+  let game: GameManager;
+
+  beforeAll(() => {
+    phaserGame = new Phaser.Game({
+      type: Phaser.HEADLESS,
+    });
+  });
+
+  afterEach(() => {
+    game.phaseInterceptor.restoreOg();
+  });
+
+  beforeEach(() => {
+    game = new GameManager(phaserGame);
+    game.override
+      .moveset(Moves.SPLASH)
+      .ability(Abilities.NO_GUARD)
+      .battleStyle("single")
+      .disableCrits()
+      .enemyLevel(100)
+      .enemySpecies(Species.MAGIKARP)
+      .enemyAbility(Abilities.BALL_FETCH)
+      .enemyMoveset(Moves.SPLASH);
+  });
+
+  function onlyUnique<T>(array: T[]): T[] {
+    return [...new Set<T>(array)];
+  }
+
+  // TODO: We currently generate IDs as a pure random integer; remove once unique UUIDs are added
+  it.todo("2 Pokemon should not be able to generate with the same ID during 1 encounter", async () => {
+    game.override.battleType(BattleType.TRAINER); // enemy generates 2 mons
+    await game.classicMode.startBattle([Species.FEEBAS, Species.ABRA]);
+
+    const ids = (game.scene.getPlayerParty() as Pokemon[]).concat(game.scene.getEnemyParty()).map((p: Pokemon) => p.id);
+    const uniqueIds = onlyUnique(ids);
+
+    expect(ids).toHaveLength(uniqueIds.length);
+  });
+
+  it("should not prevent item theft with PID of 0", async () => {
+    game.override
+      .moveset([Moves.THIEF, Moves.SPLASH])
+      .enemyHeldItems([{ name: "BERRY", count: 1, type: BerryType.APICOT }]);
+
+    vi.spyOn(allMoves[Moves.THIEF], "chance", "get").mockReturnValue(100);
+
+    await game.classicMode.startBattle([Species.TREECKO]);
+
+    const player = game.scene.getPlayerPokemon()!;
+    const enemy = game.scene.getEnemyPokemon()!;
+    // Override enemy pokemon PID to be 0
+    enemy.id = 0;
+    game.scene.getModifiers(BerryModifier, false).forEach(modifier => {
+      modifier.pokemonId = enemy.id;
+    });
+
+    expect(enemy.getHeldItems()).toHaveLength(1);
+    expect(player.getHeldItems()).toHaveLength(0);
+
+    // Player uses Thief and steals the opponent's item
+    game.move.select(Moves.THIEF);
+    await game.phaseInterceptor.to("TurnEndPhase");
+
+    expect(enemy.getHeldItems()).toHaveLength(0);
+    expect(player.getHeldItems()).toHaveLength(1);
+  });
+
+  it("should not prevent Syrup Bomb triggering if user has PID of 0", async () => {
+    game.override.moveset(Moves.SYRUP_BOMB);
+    await game.classicMode.startBattle([Species.TREECKO]);
+
+    const player = game.scene.getPlayerPokemon()!;
+    // Override player pokemon PID to be 0
+    player.id = 0;
+
+    const enemy = game.scene.getEnemyPokemon()!;
+    expect(enemy.getTag(BattlerTagType.SYRUP_BOMB)).toBeUndefined();
+
+    game.move.select(Moves.SYRUP_BOMB);
+    await game.phaseInterceptor.to("TurnEndPhase");
+
+    const syrupTag = enemy.getTag(BattlerTagType.SYRUP_BOMB)!;
+    expect(syrupTag).toBeDefined();
+    expect(syrupTag.getSourcePokemon()).toBe(player);
+    expect(enemy.getStatStage(Stat.SPD)).toBe(-1);
+  });
+});