diff --git a/src/data/mystery-encounters/encounters/dark-deal-encounter.ts b/src/data/mystery-encounters/encounters/dark-deal-encounter.ts
index 4f7d5406dc3..df4eefc887e 100644
--- a/src/data/mystery-encounters/encounters/dark-deal-encounter.ts
+++ b/src/data/mystery-encounters/encounters/dark-deal-encounter.ts
@@ -164,9 +164,9 @@ export const DarkDealEncounter: MysteryEncounter =
           // Start encounter with random legendary (7-10 starter strength) that has level additive
           // If this is a mono-type challenge, always ensure the required type is filtered for
           let bossTypes: Type[] = encounter.misc.removedTypes;
-          const singleTypeChallenges = scene.gameMode.challenges.filter(c => c.id === Challenges.SINGLE_TYPE);
+          const singleTypeChallenges = scene.gameMode.challenges.filter(c => c.value && c.id === Challenges.SINGLE_TYPE);
           if (scene.gameMode.isChallenge && singleTypeChallenges.length > 0) {
-            bossTypes = singleTypeChallenges.map(c => c.value as Type);
+            bossTypes = singleTypeChallenges.map(c => (c.value - 1) as Type);
           }
 
           const bossModifiers: PokemonHeldItemModifier[] = encounter.misc.modifiers;
diff --git a/src/data/mystery-encounters/encounters/delibirdy-encounter.ts b/src/data/mystery-encounters/encounters/delibirdy-encounter.ts
index 006ab81851b..d5f9388b56c 100644
--- a/src/data/mystery-encounters/encounters/delibirdy-encounter.ts
+++ b/src/data/mystery-encounters/encounters/delibirdy-encounter.ts
@@ -199,7 +199,7 @@ export const DelibirdyEncounter: MysteryEncounter =
           const encounter = scene.currentBattle.mysteryEncounter!;
           const modifier: BerryModifier | HealingBoosterModifier = encounter.misc.chosenModifier;
 
-          // Give the player a Candy Jar if they gave a Berry, and a Healing Charm for Reviver Seed
+          // Give the player a Candy Jar if they gave a Berry, and a Berry Pouch for Reviver Seed
           if (modifier instanceof BerryModifier) {
             // Check if the player has max stacks of that Candy Jar already
             const existing = scene.findModifier(m => m instanceof LevelIncrementBoosterModifier) as LevelIncrementBoosterModifier;
@@ -214,7 +214,7 @@ export const DelibirdyEncounter: MysteryEncounter =
               scene.unshiftPhase(new ModifierRewardPhase(scene, modifierTypes.CANDY_JAR));
             }
           } else {
-            // Check if the player has max stacks of that Healing Charm already
+            // Check if the player has max stacks of that Berry Pouch already
             const existing = scene.findModifier(m => m instanceof PreserveBerryModifier) as PreserveBerryModifier;
 
             if (existing && existing.getStackCount() >= existing.getMaxStackCount(scene)) {
diff --git a/src/data/mystery-encounters/encounters/fiery-fallout-encounter.ts b/src/data/mystery-encounters/encounters/fiery-fallout-encounter.ts
index 266ba3c38ef..5c16e5d8564 100644
--- a/src/data/mystery-encounters/encounters/fiery-fallout-encounter.ts
+++ b/src/data/mystery-encounters/encounters/fiery-fallout-encounter.ts
@@ -71,7 +71,7 @@ export const FieryFalloutEncounter: MysteryEncounter =
             gender: Gender.MALE,
             tags: [ BattlerTagType.MYSTERY_ENCOUNTER_POST_SUMMON ],
             mysteryEncounterBattleEffects: (pokemon: Pokemon) => {
-              pokemon.scene.unshiftPhase(new StatStageChangePhase(pokemon.scene, pokemon.getBattlerIndex(), true, [ Stat.SPDEF, Stat.SPD ], 2));
+              pokemon.scene.unshiftPhase(new StatStageChangePhase(pokemon.scene, pokemon.getBattlerIndex(), true, [ Stat.SPDEF, Stat.SPD ], 1));
             }
           },
           {
@@ -80,7 +80,7 @@ export const FieryFalloutEncounter: MysteryEncounter =
             gender: Gender.FEMALE,
             tags: [ BattlerTagType.MYSTERY_ENCOUNTER_POST_SUMMON ],
             mysteryEncounterBattleEffects: (pokemon: Pokemon) => {
-              pokemon.scene.unshiftPhase(new StatStageChangePhase(pokemon.scene, pokemon.getBattlerIndex(), true, [ Stat.SPDEF, Stat.SPD ], 2));
+              pokemon.scene.unshiftPhase(new StatStageChangePhase(pokemon.scene, pokemon.getBattlerIndex(), true, [ Stat.SPDEF, Stat.SPD ], 1));
             }
           }
         ],
@@ -259,9 +259,14 @@ function giveLeadPokemonAttackTypeBoostItem(scene: BattleScene) {
   // Give first party pokemon attack type boost item for free at end of battle
   const leadPokemon = scene.getParty()?.[0];
   if (leadPokemon) {
-    const encounter = scene.currentBattle.mysteryEncounter!;
-    const boosterModifierType = generateModifierType(scene, modifierTypes.ATTACK_TYPE_BOOSTER) as AttackTypeBoosterModifierType;
+    // Generate type booster held item, default to Charcoal if item fails to generate
+    let boosterModifierType = generateModifierType(scene, modifierTypes.ATTACK_TYPE_BOOSTER) as AttackTypeBoosterModifierType;
+    if (!boosterModifierType) {
+      boosterModifierType = generateModifierType(scene, modifierTypes.ATTACK_TYPE_BOOSTER, [ Type.FIRE ]) as AttackTypeBoosterModifierType;
+    }
     applyModifierTypeToPlayerPokemon(scene, leadPokemon, boosterModifierType);
+
+    const encounter = scene.currentBattle.mysteryEncounter!;
     encounter.setDialogueToken("itemName", boosterModifierType.name);
     encounter.setDialogueToken("leadPokemon", leadPokemon.getNameToRender());
     queueEncounterMessage(scene, `${namespace}:found_item`);
diff --git a/src/data/mystery-encounters/requirements/requirement-groups.ts b/src/data/mystery-encounters/requirements/requirement-groups.ts
index 3eac6806407..76bbb8f03a7 100644
--- a/src/data/mystery-encounters/requirements/requirement-groups.ts
+++ b/src/data/mystery-encounters/requirements/requirement-groups.ts
@@ -130,5 +130,8 @@ export const FIRE_RESISTANT_ABILITIES = [
   Abilities.THERMAL_EXCHANGE,
   Abilities.THICK_FAT,
   Abilities.WATER_BUBBLE,
-  Abilities.MAGMA_ARMOR
+  Abilities.MAGMA_ARMOR,
+  Abilities.WATER_VEIL,
+  Abilities.STEAM_ENGINE,
+  Abilities.PRIMORDIAL_SEA
 ];
diff --git a/src/phases/select-modifier-phase.ts b/src/phases/select-modifier-phase.ts
index f7bac4373b9..e5a60692bb4 100644
--- a/src/phases/select-modifier-phase.ts
+++ b/src/phases/select-modifier-phase.ts
@@ -276,7 +276,7 @@ export class SelectModifierPhase extends BattlePhase {
       multiplier = this.customModifierSettings.rerollMultiplier;
     }
 
-    const baseMultiplier = Math.min(Math.ceil(this.scene.currentBattle.waveIndex / 10) * baseValue * (this.rerollCount ** 2) * multiplier, Number.MAX_SAFE_INTEGER);
+    const baseMultiplier = Math.min(Math.ceil(this.scene.currentBattle.waveIndex / 10) * baseValue * (2 ** this.rerollCount) * multiplier, Number.MAX_SAFE_INTEGER);
 
     // Apply Black Sludge to reroll cost
     const modifiedRerollCost = new NumberHolder(baseMultiplier);
diff --git a/src/system/pokemon-data.ts b/src/system/pokemon-data.ts
index d07f759ba02..0e211643f29 100644
--- a/src/system/pokemon-data.ts
+++ b/src/system/pokemon-data.ts
@@ -116,6 +116,8 @@ export default class PokemonData {
 
     this.customPokemonData = new CustomPokemonData(source.customPokemonData);
 
+    // Deprecated, but needed for session data migration
+    this.natureOverride = source.natureOverride;
     this.mysteryEncounterPokemonData = new CustomPokemonData(source.mysteryEncounterPokemonData);
     this.fusionMysteryEncounterPokemonData = new CustomPokemonData(source.fusionMysteryEncounterPokemonData);