diff --git a/src/data/battler-tags.ts b/src/data/battler-tags.ts
index 66bcc7b9c3c..67abb9d9ba8 100644
--- a/src/data/battler-tags.ts
+++ b/src/data/battler-tags.ts
@@ -1863,6 +1863,30 @@ export class ExposedTag extends BattlerTag {
   }
 }
 
+/**
+ * Tag that doubles the type effectiveness of a move.
+ * @extends BattlerTag
+ */
+export class DoubleMoveTypeEffectivenessTag extends BattlerTag {
+  /** The move's type effectiveness to be doubled. */
+  public moveType: Type;
+
+  constructor(moveType: Type, tagType: BattlerTagType, lapseType: BattlerTagLapseType, sourceMove: Moves) {
+    super(tagType, lapseType, 1, sourceMove);
+
+    this.moveType = moveType;
+  }
+
+  /**
+   * If the Pokemon is terastallized, the tag cannot be added.
+   * @param pokemon the pokemon to which the tag is added
+   * @returns whether the tag is applied
+   */
+  canAdd(pokemon: Pokemon): boolean {
+    return !pokemon.isTerastallized();
+  }
+}
+
 
 export function getBattlerTag(tagType: BattlerTagType, turnCount: number, sourceMove: Moves, sourceId: number): BattlerTag {
   switch (tagType) {
@@ -2002,6 +2026,8 @@ export function getBattlerTag(tagType: BattlerTagType, turnCount: number, source
   case BattlerTagType.GULP_MISSILE_ARROKUDA:
   case BattlerTagType.GULP_MISSILE_PIKACHU:
     return new GulpMissileTag(tagType, sourceMove);
+  case BattlerTagType.TAR_SHOT:
+    return new DoubleMoveTypeEffectivenessTag(Type.FIRE, tagType, BattlerTagLapseType.CUSTOM, sourceMove);
   case BattlerTagType.NONE:
   default:
     return new BattlerTag(tagType, BattlerTagLapseType.CUSTOM, turnCount, sourceMove, sourceId);
diff --git a/src/data/move.ts b/src/data/move.ts
index ddf043c554d..a8f98a0ca04 100644
--- a/src/data/move.ts
+++ b/src/data/move.ts
@@ -8692,7 +8692,7 @@ export function initMoves() {
       .condition((user, target, move) => user.getTag(TrappedTag)?.sourceMove !== Moves.NO_RETREAT), // fails if the user is currently trapped by No Retreat
     new StatusMove(Moves.TAR_SHOT, Type.ROCK, 100, 15, -1, 0, 8)
       .attr(StatStageChangeAttr, [ Stat.SPD ], -1)
-      .partial(),
+      .attr(AddBattlerTagAttr, BattlerTagType.TAR_SHOT, false),
     new StatusMove(Moves.MAGIC_POWDER, Type.PSYCHIC, 100, 20, -1, 0, 8)
       .attr(ChangeTypeAttr, Type.PSYCHIC)
       .powderMove(),
diff --git a/src/enums/battler-tag-type.ts b/src/enums/battler-tag-type.ts
index 20ceb1b331f..88b3070fe15 100644
--- a/src/enums/battler-tag-type.ts
+++ b/src/enums/battler-tag-type.ts
@@ -72,4 +72,5 @@ export enum BattlerTagType {
   SHELL_TRAP = "SHELL_TRAP",
   DRAGON_CHEER = "DRAGON_CHEER",
   NO_RETREAT = "NO_RETREAT",
+  TAR_SHOT = "TAR_SHOT",
 }
diff --git a/src/field/pokemon.ts b/src/field/pokemon.ts
index e0a9a4a86ce..ae4d015454d 100644
--- a/src/field/pokemon.ts
+++ b/src/field/pokemon.ts
@@ -17,7 +17,7 @@ import { initMoveAnim, loadMoveAnimAssets } from "../data/battle-anims";
 import { Status, StatusEffect, getRandomStatus } from "../data/status-effect";
 import { pokemonEvolutions, pokemonPrevolutions, SpeciesFormEvolution, SpeciesEvolutionCondition, FusionSpeciesFormEvolution } from "../data/pokemon-evolutions";
 import { reverseCompatibleTms, tmSpecies, tmPoolTiers } from "../data/tms";
-import { BattlerTag, BattlerTagLapseType, EncoreTag, GroundedTag, HighestStatBoostTag, TypeImmuneTag, getBattlerTag, SemiInvulnerableTag, TypeBoostTag, ExposedTag, DragonCheerTag, CritBoostTag, TrappedTag } from "../data/battler-tags";
+import { BattlerTag, BattlerTagLapseType, EncoreTag, GroundedTag, HighestStatBoostTag, TypeImmuneTag, getBattlerTag, SemiInvulnerableTag, TypeBoostTag, ExposedTag, DragonCheerTag, CritBoostTag, TrappedTag, DoubleMoveTypeEffectivenessTag } from "../data/battler-tags";
 import { WeatherType } from "../data/weather";
 import { ArenaTagSide, NoCritTag, WeakenMoveScreenTag } from "../data/arena-tag";
 import { Ability, AbAttr, StatMultiplierAbAttr, BlockCritAbAttr, BonusCritAbAttr, BypassBurnDamageReductionAbAttr, FieldPriorityMoveImmunityAbAttr, IgnoreOpponentStatStagesAbAttr, MoveImmunityAbAttr, PreDefendFullHpEndureAbAttr, ReceivedMoveDamageMultiplierAbAttr, ReduceStatusEffectDurationAbAttr, StabBoostAbAttr, StatusEffectImmunityAbAttr, TypeImmunityAbAttr, WeightMultiplierAbAttr, allAbilities, applyAbAttrs, applyStatMultiplierAbAttrs, applyPreApplyBattlerTagAbAttrs, applyPreAttackAbAttrs, applyPreDefendAbAttrs, applyPreSetStatusAbAttrs, UnsuppressableAbilityAbAttr, SuppressFieldAbilitiesAbAttr, NoFusionAbilityAbAttr, MultCritAbAttr, IgnoreTypeImmunityAbAttr, DamageBoostAbAttr, IgnoreTypeStatusEffectImmunityAbAttr, ConditionalCritAbAttr, applyFieldStatMultiplierAbAttrs, FieldMultiplyStatAbAttr, AddSecondStrikeAbAttr, UserFieldStatusEffectImmunityAbAttr, UserFieldBattlerTagImmunityAbAttr, BattlerTagImmunityAbAttr, MoveTypeChangeAbAttr, FullHpResistTypeAbAttr, applyCheckTrappedAbAttrs, CheckTrappedAbAttr } from "../data/ability";
@@ -1348,7 +1348,7 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
 
   /**
    * Calculates the effectiveness of a move against the Pokémon.
-   *
+   * This includes modifiers from move and ability attributes.
    * @param source {@linkcode Pokemon} The attacking Pokémon.
    * @param move {@linkcode Move} The move being used by the attacking Pokémon.
    * @param ignoreAbility Whether to ignore abilities that might affect type effectiveness or immunity (defaults to `false`).
@@ -1372,6 +1372,11 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
       typeMultiplier.value = 0;
     }
 
+    const doubleMoveTypeEffectiveness = this.getTag(DoubleMoveTypeEffectivenessTag);
+    if (doubleMoveTypeEffectiveness && doubleMoveTypeEffectiveness.moveType === this.getMoveType(move)) {
+      typeMultiplier.value *= 2;
+    }
+
     const cancelledHolder = cancelled ?? new Utils.BooleanHolder(false);
     if (!ignoreAbility) {
       applyPreDefendAbAttrs(TypeImmunityAbAttr, this, source, move, cancelledHolder, simulated, typeMultiplier);
@@ -1403,7 +1408,7 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
   }
 
   /**
-   * Calculates the type effectiveness multiplier for an attack type
+   * Calculates the move's type effectiveness multiplier based on the target's type/s.
    * @param moveType {@linkcode Type} the type of the move being used
    * @param source {@linkcode Pokemon} the Pokemon using the move
    * @param ignoreStrongWinds whether or not this ignores strong winds (anticipation, forewarn, stealth rocks)
diff --git a/src/test/moves/tar_shot.test.ts b/src/test/moves/tar_shot.test.ts
new file mode 100644
index 00000000000..03aed78bef2
--- /dev/null
+++ b/src/test/moves/tar_shot.test.ts
@@ -0,0 +1,88 @@
+import { BattlerIndex } from "#app/battle.js";
+import { Moves } from "#app/enums/moves.js";
+import { Species } from "#app/enums/species.js";
+import { Stat } from "#app/enums/stat.js";
+import { Abilities } from "#enums/abilities";
+import GameManager from "#test/utils/gameManager";
+import { SPLASH_ONLY } from "#test/utils/testUtils";
+import Phaser from "phaser";
+import { afterEach, beforeAll, beforeEach, describe, expect, it, vi } from "vitest";
+
+describe("Moves - Tar Shot", () => {
+  let phaserGame: Phaser.Game;
+  let game: GameManager;
+  const TIMEOUT = 20 * 1000;
+
+  beforeAll(() => {
+    phaserGame = new Phaser.Game({
+      type: Phaser.HEADLESS,
+    });
+  });
+
+  afterEach(() => {
+    game.phaseInterceptor.restoreOg();
+  });
+
+  beforeEach(() => {
+    game = new GameManager(phaserGame);
+    game.override
+      .battleType("single")
+      .enemyAbility(Abilities.BALL_FETCH)
+      .enemyMoveset(SPLASH_ONLY)
+      .enemySpecies(Species.TANGELA)
+      .enemyLevel(10)
+      .moveset([Moves.TAR_SHOT, Moves.FIRE_PUNCH])
+      .disableCrits();
+  });
+
+  it("lowers the target's Speed stat by one stage and doubles the effectiveness of Fire-type moves used on the target", async () => {
+    await game.classicMode.startBattle([Species.PIKACHU]);
+
+    const enemy = game.scene.getEnemyPokemon()!;
+
+    vi.spyOn(enemy, "getMaxHp").mockReturnValue(1000);
+    vi.spyOn(enemy, "getMoveEffectiveness");
+
+    game.move.select(Moves.TAR_SHOT);
+
+    await game.phaseInterceptor.to("TurnEndPhase");
+    expect(enemy.getStatStage(Stat.SPD)).toBe(-1);
+
+    await game.toNextTurn();
+
+    game.move.select(Moves.FIRE_PUNCH);
+    await game.setTurnOrder([BattlerIndex.PLAYER, BattlerIndex.ENEMY]);
+
+    await game.phaseInterceptor.to("MoveEndPhase");
+    expect(enemy.getMoveEffectiveness).toHaveReturnedWith(4);
+  }, TIMEOUT);
+
+  it("will not double the effectiveness of Fire-type moves used on a target that is already under the effect of Tar Shot (but may still lower its Speed)", async () => {
+    await game.classicMode.startBattle([Species.PIKACHU]);
+
+    const enemy = game.scene.getEnemyPokemon()!;
+
+    vi.spyOn(enemy, "getMaxHp").mockReturnValue(1000);
+    vi.spyOn(enemy, "getMoveEffectiveness");
+
+    game.move.select(Moves.TAR_SHOT);
+
+    await game.phaseInterceptor.to("TurnEndPhase");
+    expect(enemy.getStatStage(Stat.SPD)).toBe(-1);
+
+    await game.toNextTurn();
+
+    game.move.select(Moves.TAR_SHOT);
+
+    await game.phaseInterceptor.to("TurnEndPhase");
+    expect(enemy.getStatStage(Stat.SPD)).toBe(-2);
+
+    await game.toNextTurn();
+
+    game.move.select(Moves.FIRE_PUNCH);
+    await game.setTurnOrder([BattlerIndex.PLAYER, BattlerIndex.ENEMY]);
+
+    await game.phaseInterceptor.to("MoveEndPhase");
+    expect(enemy.getMoveEffectiveness).toHaveReturnedWith(4);
+  }, TIMEOUT);
+});