diff --git a/src/data/move.ts b/src/data/move.ts
index d547cd565248..8c9e8b0fb991 100644
--- a/src/data/move.ts
+++ b/src/data/move.ts
@@ -3942,7 +3942,14 @@ export class PhotonGeyserCategoryAttr extends VariableMoveCategoryAttr {
   }
 }
 
-export class TeraBlastCategoryAttr extends VariableMoveCategoryAttr {
+/**
+ * Attribute used for tera moves that change category based on the user's Atk and SpAtk stats
+ * Note: Currently, `getEffectiveStat` does not ignore all abilities that affect stats except those
+ * with the attribute of `StatMultiplierAbAttr`
+ * TODO: Remove the `.partial()` tag from Tera Blast and Tera Starstorm when the above issue is resolved
+ * @extends VariableMoveCategoryAttr
+ */
+export class TeraMoveCategoryAttr extends VariableMoveCategoryAttr {
   apply(user: Pokemon, target: Pokemon, move: Move, args: any[]): boolean {
     const category = (args[0] as Utils.NumberHolder);
 
@@ -4031,6 +4038,30 @@ export class VariableMoveTypeAttr extends MoveAttr {
   }
 }
 
+/**
+ * Attribute used for Tera Starstorm that changes the move type to Stellar
+ * @extends VariableMoveTypeAttr
+ */
+export class TeraStarstormTypeAttr extends VariableMoveTypeAttr {
+  /**
+   *
+   * @param user the {@linkcode Pokemon} using the move
+   * @param target n/a
+   * @param move n/a
+   * @param args[0] {@linkcode Utils.NumberHolder} the move type
+   * @returns `true` if the move type is changed to {@linkcode Type.STELLAR}, `false` otherwise
+   */
+  override apply(user: Pokemon, target: Pokemon, move: Move, args: any[]): boolean {
+    if (user.isTerastallized() && (user.hasFusionSpecies(Species.TERAPAGOS) || user.species.speciesId === Species.TERAPAGOS)) {
+      const moveType = args[0] as Utils.NumberHolder;
+
+      moveType.value = Type.STELLAR;
+      return true;
+    }
+    return false;
+  }
+}
+
 export class FormChangeItemTypeAttr extends VariableMoveTypeAttr {
   apply(user: Pokemon, target: Pokemon, move: Move, args: any[]): boolean {
     const moveType = args[0];
@@ -9190,7 +9221,7 @@ export function initMoves() {
       .attr(HalfSacrificialAttr),
     new AttackMove(Moves.EXPANDING_FORCE, Type.PSYCHIC, MoveCategory.SPECIAL, 80, 100, 10, -1, 0, 8)
       .attr(MovePowerMultiplierAttr, (user, target, move) => user.scene.arena.getTerrainType() === TerrainType.PSYCHIC && user.isGrounded() ? 1.5 : 1)
-      .attr(VariableTargetAttr, (user, target, move) => user.scene.arena.getTerrainType() === TerrainType.PSYCHIC && user.isGrounded() ? 6 : 3),
+      .attr(VariableTargetAttr, (user, target, move) => user.scene.arena.getTerrainType() === TerrainType.PSYCHIC && user.isGrounded() ? MoveTarget.ALL_NEAR_ENEMIES : MoveTarget.NEAR_OTHER),
     new AttackMove(Moves.STEEL_ROLLER, Type.STEEL, MoveCategory.PHYSICAL, 130, 100, 5, -1, 0, 8)
       .attr(ClearTerrainAttr)
       .condition((user, target, move) => !!user.scene.arena.terrain),
@@ -9464,10 +9495,11 @@ export function initMoves() {
       .unimplemented(),
     End Unused */
     new AttackMove(Moves.TERA_BLAST, Type.NORMAL, MoveCategory.SPECIAL, 80, 100, 10, -1, 0, 9)
-      .attr(TeraBlastCategoryAttr)
+      .attr(TeraMoveCategoryAttr)
       .attr(TeraBlastTypeAttr)
       .attr(TeraBlastPowerAttr)
-      .attr(StatStageChangeAttr, [ Stat.ATK, Stat.SPATK ], -1, true, (user, target, move) => user.isTerastallized() && user.isOfType(Type.STELLAR)),
+      .attr(StatStageChangeAttr, [ Stat.ATK, Stat.SPATK ], -1, true, (user, target, move) => user.isTerastallized() && user.isOfType(Type.STELLAR))
+      .partial(), /** Does not ignore abilities that affect stats, relevant in determining the move's category {@see TeraMoveCategoryAttr} */
     new SelfStatusMove(Moves.SILK_TRAP, Type.BUG, -1, 10, -1, 4, 9)
       .attr(ProtectAttr, BattlerTagType.SILK_TRAP)
       .condition(failIfLastCondition),
@@ -9657,8 +9689,10 @@ export function initMoves() {
       .attr(ElectroShotChargeAttr)
       .ignoresVirtual(),
     new AttackMove(Moves.TERA_STARSTORM, Type.NORMAL, MoveCategory.SPECIAL, 120, 100, 5, -1, 0, 9)
-      .attr(TeraBlastCategoryAttr)
-      .partial(),
+      .attr(TeraMoveCategoryAttr)
+      .attr(TeraStarstormTypeAttr)
+      .attr(VariableTargetAttr, (user, target, move) => (user.hasFusionSpecies(Species.TERAPAGOS) || user.species.speciesId === Species.TERAPAGOS) && user.isTerastallized() ? MoveTarget.ALL_NEAR_ENEMIES : MoveTarget.NEAR_OTHER)
+      .partial(), /** Does not ignore abilities that affect stats, relevant in determining the move's category {@see TeraMoveCategoryAttr} */
     new AttackMove(Moves.FICKLE_BEAM, Type.DRAGON, MoveCategory.SPECIAL, 80, 100, 5, 30, 0, 9)
       .attr(PreMoveMessageAttr, doublePowerChanceMessageFunc)
       .attr(DoublePowerChanceAttr),
diff --git a/src/field/pokemon.ts b/src/field/pokemon.ts
index d54114962236..de18dfb74eb0 100644
--- a/src/field/pokemon.ts
+++ b/src/field/pokemon.ts
@@ -1087,6 +1087,15 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
     return !!this.fusionSpecies;
   }
 
+  /**
+   * Checks if the {@linkcode Pokemon} has a fusion with the specified {@linkcode Species}.
+   * @param species the pokemon {@linkcode Species} to check
+   * @returns `true` if the {@linkcode Pokemon} has a fusion with the specified {@linkcode Species}, `false` otherwise
+   */
+  hasFusionSpecies(species: Species): boolean {
+    return this.fusionSpecies?.speciesId === species;
+  }
+
   abstract isBoss(): boolean;
 
   getMoveset(ignoreOverride?: boolean): (PokemonMove | null)[] {
diff --git a/src/test/moves/tera_starstorm.test.ts b/src/test/moves/tera_starstorm.test.ts
new file mode 100644
index 000000000000..20dbc0b77d6e
--- /dev/null
+++ b/src/test/moves/tera_starstorm.test.ts
@@ -0,0 +1,98 @@
+import { BattlerIndex } from "#app/battle";
+import { Type } from "#app/data/type";
+import { Abilities } from "#enums/abilities";
+import { Moves } from "#enums/moves";
+import { Species } from "#enums/species";
+import GameManager from "#test/utils/gameManager";
+import Phaser from "phaser";
+import { afterEach, beforeAll, beforeEach, describe, it, expect, vi } from "vitest";
+
+describe("Moves - Tera Starstorm", () => {
+  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.TERA_STARSTORM, Moves.SPLASH])
+      .battleType("double")
+      .enemyAbility(Abilities.BALL_FETCH)
+      .enemyMoveset(Moves.SPLASH)
+      .enemyLevel(30)
+      .enemySpecies(Species.MAGIKARP)
+      .startingHeldItems([{ name: "TERA_SHARD", type: Type.FIRE }]);
+  });
+
+  it("changes type to Stellar when used by Terapagos in its Stellar Form", async () => {
+    game.override.battleType("single");
+    await game.classicMode.startBattle([Species.TERAPAGOS]);
+
+    const terapagos = game.scene.getPlayerPokemon()!;
+
+    vi.spyOn(terapagos, "getMoveType");
+
+    game.move.select(Moves.TERA_STARSTORM);
+    await game.phaseInterceptor.to("TurnEndPhase");
+
+    expect(terapagos.isTerastallized()).toBe(true);
+    expect(terapagos.getMoveType).toHaveReturnedWith(Type.STELLAR);
+  });
+
+  it("targets both opponents in a double battle when used by Terapagos in its Stellar Form", async () => {
+    await game.classicMode.startBattle([Species.MAGIKARP, Species.TERAPAGOS]);
+
+    game.move.select(Moves.TERA_STARSTORM, 0, BattlerIndex.ENEMY);
+    game.move.select(Moves.TERA_STARSTORM, 1);
+
+    await game.setTurnOrder([BattlerIndex.PLAYER, BattlerIndex.PLAYER_2, BattlerIndex.ENEMY, BattlerIndex.ENEMY_2]);
+
+    const enemyField = game.scene.getEnemyField();
+
+    // Pokemon other than Terapagos should not be affected - only hits one target
+    await game.phaseInterceptor.to("MoveEndPhase");
+    expect(enemyField.some(pokemon => pokemon.isFullHp())).toBe(true);
+
+    // Terapagos in Stellar Form should hit both targets
+    await game.phaseInterceptor.to("MoveEndPhase");
+    expect(enemyField.every(pokemon => pokemon.isFullHp())).toBe(false);
+  });
+
+  it("applies the effects when Terapagos in Stellar Form is fused with another Pokemon", async () => {
+    await game.classicMode.startBattle([Species.TERAPAGOS, Species.CHARMANDER, Species.MAGIKARP]);
+
+    const fusionedMon = game.scene.getParty()[0];
+    const magikarp = game.scene.getParty()[2];
+
+    // Fuse party members (taken from PlayerPokemon.fuse(...) function)
+    fusionedMon.fusionSpecies = magikarp.species;
+    fusionedMon.fusionFormIndex = magikarp.formIndex;
+    fusionedMon.fusionAbilityIndex = magikarp.abilityIndex;
+    fusionedMon.fusionShiny = magikarp.shiny;
+    fusionedMon.fusionVariant = magikarp.variant;
+    fusionedMon.fusionGender = magikarp.gender;
+    fusionedMon.fusionLuck = magikarp.luck;
+
+    vi.spyOn(fusionedMon, "getMoveType");
+
+    game.move.select(Moves.TERA_STARSTORM, 0);
+    game.move.select(Moves.SPLASH, 1);
+    await game.phaseInterceptor.to("TurnEndPhase");
+
+    // Fusion and terastallized
+    expect(fusionedMon.isFusion()).toBe(true);
+    expect(fusionedMon.isTerastallized()).toBe(true);
+    // Move effects should be applied
+    expect(fusionedMon.getMoveType).toHaveReturnedWith(Type.STELLAR);
+    expect(game.scene.getEnemyField().every(pokemon => pokemon.isFullHp())).toBe(false);
+  });
+});