[Bug] Fix a couple small issues with uturn and friends (#3321)

* prevent double-application of status contact abilities and switch out abilities

* use SwitchPhase for ForceSwitchOutAbAttr instead of switchOut()

* add tests for baton pass/uturn

* PR comments

* Update src/test/moves/baton_pass.test.ts

* add test for forced switch after mutual KO + revive

* tweak condition to fix uturn/baton pass

* improve docs

* style/typo nits from CR

Co-authored-by: NightKev <34855794+DayKev@users.noreply.github.com>

* CR feedback

* use doSelectPartyPokemon + rename

* int -> number

Co-authored-by: Adrian T. <68144167+torranx@users.noreply.github.com>

---------

Co-authored-by: NightKev <34855794+DayKev@users.noreply.github.com>
Co-authored-by: Adrian T. <68144167+torranx@users.noreply.github.com>

src/data/move.ts

@@ -1,5 +1,5 @@
 import { ChargeAnim, MoveChargeAnim, initMoveAnim, loadMoveAnimAssets } from "./battle-anims";
-import { BattleEndPhase, MoveEndPhase, MovePhase, NewBattlePhase, PartyStatusCurePhase, PokemonHealPhase, StatChangePhase, SwitchSummonPhase } from "../phases";
+import { BattleEndPhase, MoveEndPhase, MovePhase, NewBattlePhase, PartyStatusCurePhase, PokemonHealPhase, StatChangePhase, SwitchPhase, SwitchSummonPhase } from "../phases";
 import { BattleStat, getBattleStatName } from "./battle-stat";
 import { EncoreTag, GulpMissileTag, HelpingHandTag, SemiInvulnerableTag, StockpilingTag, TypeBoostTag } from "./battler-tags";
 import { getPokemonNameWithAffix } from "../messages";
@@ -10,7 +10,7 @@ import { Constructor } from "#app/utils";
 import * as Utils from "../utils";
 import { WeatherType } from "./weather";
 import { ArenaTagSide, ArenaTrapTag, WeakenMoveTypeTag } from "./arena-tag";
-import { UnswappableAbilityAbAttr, UncopiableAbilityAbAttr, UnsuppressableAbilityAbAttr, BlockRecoilDamageAttr, BlockOneHitKOAbAttr, IgnoreContactAbAttr, MaxMultiHitAbAttr, applyAbAttrs, BlockNonDirectDamageAbAttr, applyPreSwitchOutAbAttrs, PreSwitchOutAbAttr, applyPostDefendAbAttrs, PostDefendContactApplyStatusEffectAbAttr, MoveAbilityBypassAbAttr, ReverseDrainAbAttr, FieldPreventExplosiveMovesAbAttr, ForceSwitchOutImmunityAbAttr, BlockItemTheftAbAttr, applyPostAttackAbAttrs, ConfusionOnStatusEffectAbAttr, HealFromBerryUseAbAttr, IgnoreProtectOnContactAbAttr, IgnoreMoveEffectsAbAttr, applyPreDefendAbAttrs, MoveEffectChanceMultiplierAbAttr, WonderSkinAbAttr, applyPreAttackAbAttrs, MoveTypeChangeAttr, UserFieldMoveTypePowerBoostAbAttr, FieldMoveTypePowerBoostAbAttr, AllyMoveCategoryPowerBoostAbAttr, VariableMovePowerAbAttr } from "./ability";
+import { UnswappableAbilityAbAttr, UncopiableAbilityAbAttr, UnsuppressableAbilityAbAttr, BlockRecoilDamageAttr, BlockOneHitKOAbAttr, IgnoreContactAbAttr, MaxMultiHitAbAttr, applyAbAttrs, BlockNonDirectDamageAbAttr, MoveAbilityBypassAbAttr, ReverseDrainAbAttr, FieldPreventExplosiveMovesAbAttr, ForceSwitchOutImmunityAbAttr, BlockItemTheftAbAttr, applyPostAttackAbAttrs, ConfusionOnStatusEffectAbAttr, HealFromBerryUseAbAttr, IgnoreProtectOnContactAbAttr, IgnoreMoveEffectsAbAttr, applyPreDefendAbAttrs, MoveEffectChanceMultiplierAbAttr, WonderSkinAbAttr, applyPreAttackAbAttrs, MoveTypeChangeAttr, UserFieldMoveTypePowerBoostAbAttr, FieldMoveTypePowerBoostAbAttr, AllyMoveCategoryPowerBoostAbAttr, VariableMovePowerAbAttr } from "./ability";
 import { allAbilities } from "./ability";
 import { PokemonHeldItemModifier, BerryModifier, PreserveBerryModifier, PokemonMoveAccuracyBoosterModifier, AttackTypeBoosterModifier, PokemonMultiHitModifier } from "../modifier/modifier";
 import { BattlerIndex, BattleType } from "../battle";
@@ -4806,13 +4806,15 @@ export class ForceSwitchOutAttr extends MoveEffectAttr {
     this.batonPass = !!batonPass;
   }
 
+  isBatonPass() {
+    return this.batonPass;
+  }
+
   apply(user: Pokemon, target: Pokemon, move: Move, args: any[]): Promise<boolean> {
     return new Promise(resolve => {
 
   	// Check if the move category is not STATUS or if the switch out condition is not met
       if (!this.getSwitchOutCondition()(user, target, move)) {
-  	  //Apply effects before switch out i.e. poison point, flame body, etc
-        applyPostDefendAbAttrs(PostDefendContactApplyStatusEffectAbAttr, target, user, move, null);
         return resolve(false);
       }
 
@@ -4820,10 +4822,11 @@ export class ForceSwitchOutAttr extends MoveEffectAttr {
   	// This ensures that the switch out only happens when the conditions are met
 	  const switchOutTarget = this.user ? user : target;
 	  if (switchOutTarget instanceof PlayerPokemon) {
+        switchOutTarget.leaveField(!this.batonPass);
+
         if (switchOutTarget.hp > 0) {
-          applyPreSwitchOutAbAttrs(PreSwitchOutAbAttr, switchOutTarget);
+          user.scene.prependToPhase(new SwitchPhase(user.scene, switchOutTarget.getFieldIndex(), true, true), MoveEndPhase);
-          // switchOut below sets the UI to select party(this is not a separate Phase), then adds a SwitchSummonPhase with selected 'mon
+          resolve(true);
-          (switchOutTarget as PlayerPokemon).switchOut(this.batonPass).then(() => resolve(true));
         } else {
           resolve(false);
         }

src/phases.ts

@@ -4464,11 +4464,24 @@ export class PostGameOverPhase extends Phase {
   }
 }
 
+/**
+ * Opens the party selector UI and transitions into a {@linkcode SwitchSummonPhase}
+ * for the player (if a switch would be valid for the current battle state).
+ */
 export class SwitchPhase extends BattlePhase {
   protected fieldIndex: integer;
   private isModal: boolean;
   private doReturn: boolean;
 
+  /**
+   * Creates a new SwitchPhase
+   * @param scene {@linkcode BattleScene} Current battle scene
+   * @param fieldIndex Field index to switch out
+   * @param isModal Indicates if the switch should be forced (true) or is
+   * optional (false).
+   * @param doReturn Indicates if the party member on the field should be
+   * recalled to ball or has already left the field. Passed to {@linkcode SwitchSummonPhase}.
+   */
   constructor(scene: BattleScene, fieldIndex: integer, isModal: boolean, doReturn: boolean) {
     super(scene);
 
@@ -4480,13 +4493,17 @@ export class SwitchPhase extends BattlePhase {
   start() {
     super.start();
 
-    // Skip modal switch if impossible
+    // Skip modal switch if impossible (no remaining party members that aren't in battle)
     if (this.isModal && !this.scene.getParty().filter(p => p.isAllowedInBattle() && !p.isActive(true)).length) {
       return super.end();
     }
 
-    // Skip if the fainted party member has been revived already
+    // Skip if the fainted party member has been revived already. doReturn is
-    if (this.isModal && !this.scene.getParty()[this.fieldIndex].isFainted()) {
+    // only passed as `false` from FaintPhase (as opposed to other usages such
+    // as ForceSwitchOutAttr or CheckSwitchPhase), so we only want to check this
+    // if the mon should have already been returned but is still alive and well
+    // on the field. see also; battle.test.ts
+    if (this.isModal && !this.doReturn && !this.scene.getParty()[this.fieldIndex].isFainted()) {
       return super.end();
     }
 

src/test/battle/battle.test.ts

@@ -1,9 +1,24 @@
 import { allSpecies } from "#app/data/pokemon-species";
+import { TempBattleStat } from "#app/data/temp-battle-stat.js";
 import { GameModes } from "#app/game-mode";
 import { getGameMode } from "#app/game-mode.js";
-import { CommandPhase, DamagePhase, EncounterPhase, EnemyCommandPhase, LoginPhase, SelectGenderPhase, SelectModifierPhase, SelectStarterPhase, SummonPhase, TitlePhase, TurnInitPhase, VictoryPhase } from "#app/phases";
+import {
-import GameManager from "#test/utils/gameManager";
+  BattleEndPhase,
-import { generateStarter, getMovePosition, } from "#test/utils/gameManagerUtils";
+  CommandPhase, DamagePhase,
+  EncounterPhase,
+  EnemyCommandPhase,
+  LoginPhase,
+  NextEncounterPhase,
+  SelectGenderPhase,
+  SelectModifierPhase,
+  SelectStarterPhase,
+  SummonPhase,
+  SwitchPhase,
+  TitlePhase,
+  TurnInitPhase, VictoryPhase,
+} from "#app/phases";
+import GameManager from "#app/test/utils/gameManager";
+import { generateStarter, getMovePosition, } from "#app/test/utils/gameManagerUtils";
 import { Command } from "#app/ui/command-ui-handler";
 import { Mode } from "#app/ui/ui";
 import { Abilities } from "#enums/abilities";
@@ -12,6 +27,7 @@ import { PlayerGender } from "#enums/player-gender";
 import { Species } from "#enums/species";
 import Phaser from "phaser";
 import { afterEach, beforeAll, beforeEach, describe, expect, it } from "vitest";
+import { SPLASH_ONLY } from "../utils/testUtils";
 
 describe("Test Battle Phase", () => {
   let phaserGame: Phaser.Game;
@@ -312,5 +328,31 @@ describe("Test Battle Phase", () => {
     await game.toNextWave();
     expect(game.scene.currentBattle.waveIndex).toBeGreaterThan(waveIndex);
   }, 20000);
+
+  it("does not force switch if active pokemon faints at same time as enemy mon and is revived in post-battle", async () => {
+    const moveToUse = Moves.TAKE_DOWN;
+    game.override
+      .battleType("single")
+      .starterSpecies(Species.SAWK)
+      .enemySpecies(Species.RATTATA)
+      .startingWave(1)
+      .startingLevel(100)
+      .moveset([moveToUse])
+      .enemyMoveset(SPLASH_ONLY)
+      .startingHeldItems([{ name: "TEMP_STAT_BOOSTER", type: TempBattleStat.ACC }]);
+
+    await game.startBattle();
+    game.scene.getPlayerPokemon().hp = 1;
+    game.doAttack(getMovePosition(game.scene, 0, moveToUse));
+
+    await game.phaseInterceptor.to(BattleEndPhase);
+    game.doRevivePokemon(0); // pretend max revive was picked
+    game.doSelectModifier();
+
+    game.onNextPrompt("SwitchPhase", Mode.PARTY, () => {
+      expect.fail("Switch was forced");
+    }, () => game.isCurrentPhase(NextEncounterPhase));
+    await game.phaseInterceptor.to(SwitchPhase);
+  }, 20000);
 });
 

src/test/moves/baton_pass.test.ts

@@ -0,0 +1,93 @@
+import { BattleStat } from "#app/data/battle-stat.js";
+import { PostSummonPhase, TurnEndPhase } from "#app/phases.js";
+import GameManager from "#app/test/utils/gameManager";
+import { getMovePosition } from "#app/test/utils/gameManagerUtils";
+import { Moves } from "#enums/moves";
+import { Species } from "#enums/species";
+import Phaser from "phaser";
+import { afterEach, beforeAll, beforeEach, describe, expect, it } from "vitest";
+import { SPLASH_ONLY } from "../utils/testUtils";
+
+
+describe("Moves - Baton Pass", () => {
+  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
+      .battleType("single")
+      .enemySpecies(Species.DUGTRIO)
+      .startingLevel(1)
+      .startingWave(97)
+      .moveset([Moves.BATON_PASS, Moves.NASTY_PLOT, Moves.SPLASH])
+      .enemyMoveset(SPLASH_ONLY)
+      .disableCrits();
+  });
+
+  it("passes stat stage buffs when player uses it", async() => {
+    // arrange
+    await game.startBattle([
+      Species.RAICHU,
+      Species.SHUCKLE
+    ]);
+
+    // round 1 - buff
+    game.doAttack(getMovePosition(game.scene, 0, Moves.NASTY_PLOT));
+    await game.toNextTurn();
+    expect(game.scene.getPlayerPokemon().summonData.battleStats[BattleStat.SPATK]).toEqual(2);
+
+    // round 2 - baton pass
+    game.doAttack(getMovePosition(game.scene, 0, Moves.BATON_PASS));
+    game.doSelectPartyPokemon(1);
+    await game.phaseInterceptor.to(TurnEndPhase);
+
+    // assert
+    expect(game.scene.getPlayerPokemon().species.speciesId).toEqual(Species.SHUCKLE);
+    expect(game.scene.getPlayerPokemon().summonData.battleStats[BattleStat.SPATK]).toEqual(2);
+  }, 20000);
+
+  it("passes stat stage buffs when AI uses it", async() => {
+    // arrange
+    game.override
+      .startingWave(5)
+      .enemyMoveset(new Array(4).fill([Moves.NASTY_PLOT]));
+    await game.startBattle([
+      Species.RAICHU,
+      Species.SHUCKLE
+    ]);
+
+    // round 1 - ai buffs
+    game.doAttack(getMovePosition(game.scene, 0, Moves.SPLASH));
+    await game.toNextTurn();
+
+    // round 2 - baton pass
+    game.scene.getEnemyPokemon().hp = 100;
+    game.override.enemyMoveset(new Array(4).fill(Moves.BATON_PASS));
+    game.doAttack(getMovePosition(game.scene, 0, Moves.SPLASH));
+    await game.phaseInterceptor.to(PostSummonPhase, false);
+
+    // assert
+    // check buffs are still there
+    expect(game.scene.getEnemyPokemon().summonData.battleStats[BattleStat.SPATK]).toEqual(2);
+    // confirm that a switch actually happened. can't use species because I
+    // can't find a way to override trainer parties with more than 1 pokemon species
+    expect(game.scene.getEnemyPokemon().hp).not.toEqual(100);
+    expect(game.phaseInterceptor.log.slice(-4)).toEqual([
+      "MoveEffectPhase",
+      "SwitchSummonPhase",
+      "SummonPhase",
+      "PostSummonPhase"
+    ]);
+  }, 20000);
+});

src/test/moves/u_turn.test.ts

@@ -0,0 +1,98 @@
+import { Abilities } from "#app/enums/abilities.js";
+import { SwitchPhase, TurnEndPhase } from "#app/phases";
+import GameManager from "#app/test/utils/gameManager";
+import { getMovePosition } from "#app/test/utils/gameManagerUtils";
+import { Moves } from "#enums/moves";
+import { Species } from "#enums/species";
+import Phaser from "phaser";
+import { afterEach, beforeAll, beforeEach, describe, expect, it, vi } from "vitest";
+import { StatusEffect } from "#app/enums/status-effect.js";
+import { SPLASH_ONLY } from "../utils/testUtils";
+
+describe("Moves - U-turn", () => {
+  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
+      .battleType("single")
+      .enemySpecies(Species.GENGAR)
+      .startingLevel(90)
+      .startingWave(97)
+      .moveset([Moves.U_TURN])
+      .enemyMoveset(SPLASH_ONLY)
+      .disableCrits();
+  });
+
+  it("triggers regenerator a single time when a regenerator user switches out with u-turn", async() => {
+    // arrange
+    const playerHp = 1;
+    game.override.ability(Abilities.REGENERATOR);
+    await game.startBattle([
+      Species.RAICHU,
+      Species.SHUCKLE
+    ]);
+    game.scene.getPlayerPokemon().hp = playerHp;
+
+    // act
+    game.doAttack(getMovePosition(game.scene, 0, Moves.U_TURN));
+    game.doSelectPartyPokemon(1);
+    await game.phaseInterceptor.to(TurnEndPhase);
+
+    // assert
+    expect(game.scene.getParty()[1].hp).toEqual(Math.floor(game.scene.getParty()[1].getMaxHp() * 0.33 + playerHp));
+    expect(game.phaseInterceptor.log).toContain("SwitchSummonPhase");
+    expect(game.scene.getPlayerPokemon().species.speciesId).toBe(Species.SHUCKLE);
+  }, 20000);
+
+  it("triggers rough skin on the u-turn user before a new pokemon is switched in", async() => {
+    // arrange
+    game.override.enemyAbility(Abilities.ROUGH_SKIN);
+    await game.startBattle([
+      Species.RAICHU,
+      Species.SHUCKLE
+    ]);
+
+    // act
+    game.doAttack(getMovePosition(game.scene, 0, Moves.U_TURN));
+    game.doSelectPartyPokemon(1);
+    await game.phaseInterceptor.to(SwitchPhase, false);
+
+    // assert
+    expect(game.scene.getPlayerPokemon().hp).not.toEqual(game.scene.getPlayerPokemon().getMaxHp());
+    expect(game.scene.getEnemyPokemon().battleData.abilityRevealed).toBe(true); // proxy for asserting ability activated
+    expect(game.scene.getPlayerPokemon().species.speciesId).toEqual(Species.RAICHU);
+    expect(game.phaseInterceptor.log).not.toContain("SwitchSummonPhase");
+  }, 20000);
+
+  it("triggers contact abilities on the u-turn user (eg poison point) before a new pokemon is switched in", async() => {
+    // arrange
+    game.override.enemyAbility(Abilities.POISON_POINT);
+    await game.startBattle([
+      Species.RAICHU,
+      Species.SHUCKLE
+    ]);
+    vi.spyOn(game.scene.getEnemyPokemon(), "randSeedInt").mockReturnValue(0);
+
+    // act
+    game.doAttack(getMovePosition(game.scene, 0, Moves.U_TURN));
+    await game.phaseInterceptor.to(SwitchPhase, false);
+
+    // assert
+    expect(game.scene.getPlayerPokemon().status?.effect).toEqual(StatusEffect.POISON);
+    expect(game.scene.getPlayerPokemon().species.speciesId).toEqual(Species.RAICHU);
+    expect(game.scene.getEnemyPokemon().battleData.abilityRevealed).toBe(true); // proxy for asserting ability activated
+    expect(game.phaseInterceptor.log).not.toContain("SwitchSummonPhase");
+  }, 20000);
+});

src/test/utils/gameManager.ts

@@ -1,7 +1,7 @@
 import GameWrapper from "#test/utils/gameWrapper";
 import { Mode } from "#app/ui/ui";
 import { generateStarter, waitUntil } from "#test/utils/gameManagerUtils";
-import { CommandPhase, EncounterPhase, FaintPhase, LoginPhase, NewBattlePhase, SelectStarterPhase, SelectTargetPhase, TitlePhase, TurnEndPhase, TurnInitPhase, TurnStartPhase } from "#app/phases";
+import { CommandPhase, EncounterPhase, FaintPhase, LoginPhase, MovePhase, NewBattlePhase, SelectStarterPhase, SelectTargetPhase, TitlePhase, TurnEndPhase, TurnInitPhase, TurnStartPhase } from "#app/phases";
 import BattleScene from "#app/battle-scene.js";
 import PhaseInterceptor from "#test/utils/phaseInterceptor";
 import TextInterceptor from "#test/utils/TextInterceptor";
@@ -9,13 +9,12 @@ import { GameModes, getGameMode } from "#app/game-mode";
 import fs from "fs";
 import { AES, enc } from "crypto-js";
 import { updateUserInfo } from "#app/account";
-import InputsHandler from "#test/utils/inputsHandler";
+import InputsHandler from "#app/test/utils/inputsHandler";
-import ErrorInterceptor from "#test/utils/errorInterceptor";
+import ErrorInterceptor from "#app/test/utils/errorInterceptor";
 import { EnemyPokemon, PlayerPokemon } from "#app/field/pokemon";
-import { MockClock } from "#test/utils/mocks/mockClock";
+import { MockClock } from "#app/test/utils/mocks/mockClock";
-import { Command } from "#app/ui/command-ui-handler";
+import PartyUiHandler from "#app/ui/party-ui-handler";
-import ModifierSelectUiHandler from "#app/ui/modifier-select-ui-handler";
+import CommandUiHandler, { Command } from "#app/ui/command-ui-handler";
-import PartyUiHandler, { PartyUiMode } from "#app/ui/party-ui-handler";
 import Trainer from "#app/field/trainer";
 import { ExpNotification } from "#enums/exp-notification";
 import { GameDataType } from "#enums/game-data-type";
@@ -28,6 +27,7 @@ import { OverridesHelper } from "./overridesHelper";
 import { ModifierTypeOption, modifierTypes } from "#app/modifier/modifier-type.js";
 import overrides from "#app/overrides.js";
 import { removeEnemyHeldItems } from "./testUtils";
+import ModifierSelectUiHandler from "#app/ui/modifier-select-ui-handler.js";
 
 /**
  * Class to manage the game state and transitions between phases.
@@ -178,7 +178,7 @@ export default class GameManager {
       if (move.isMultiTarget()) {
         handler.processInput(Button.ACTION);
       }
-    }, () => this.isCurrentPhase(CommandPhase) || this.isCurrentPhase(TurnEndPhase));
+    }, () => this.isCurrentPhase(CommandPhase) || this.isCurrentPhase(MovePhase) || this.isCurrentPhase(TurnEndPhase));
   }
 
   /**
@@ -313,20 +313,20 @@ export default class GameManager {
   }
 
   /**
-   * Switch pokemon and transition to the enemy command phase
+   * Command an in-battle switch to another Pokemon via the main battle menu.
    * @param pokemonIndex the index of the pokemon in your party to switch to
    */
   doSwitchPokemon(pokemonIndex: number) {
     this.onNextPrompt("CommandPhase", Mode.COMMAND, () => {
-      this.scene.ui.setMode(Mode.PARTY, PartyUiMode.SWITCH, (this.scene.getCurrentPhase() as CommandPhase).getPokemon().getFieldIndex(), null, PartyUiHandler.FilterNonFainted);
+      (this.scene.ui.getHandler() as CommandUiHandler).setCursor(2);
-    });
+      (this.scene.ui.getHandler() as CommandUiHandler).processInput(Button.ACTION);
-    this.onNextPrompt("CommandPhase", Mode.PARTY, () => {
-      (this.scene.getCurrentPhase() as CommandPhase).handleCommand(Command.POKEMON, pokemonIndex, false);
     });
+
+    this.doSelectPartyPokemon(pokemonIndex, "CommandPhase");
   }
 
   /**
-   * Revive pokemon, currently player's only.
+   * Revive pokemon, currently players only.
    * @param pokemonIndex the index of the pokemon in your party to revive
    */
   doRevivePokemon(pokemonIndex: number) {
@@ -335,4 +335,23 @@ export default class GameManager {
     const modifier = candidate.type.newModifier(party[pokemonIndex]);
     this.scene.addModifier(modifier, false);
   }
+
+  /**
+   * Select a pokemon from the party menu. Only really handles the basic cases
+   * of the party UI, where you just need to navigate to a party slot and press
+   * Action twice - navigating any menus that come up after you select a party member
+   * is not supported.
+   * @param slot the index of the pokemon in your party to switch to
+   * @param inPhase Which phase to expect the selection to occur in. Typically
+   * non-command switch actions happen in SwitchPhase.
+   */
+  doSelectPartyPokemon(slot: number, inPhase = "SwitchPhase") {
+    this.onNextPrompt(inPhase, Mode.PARTY, () => {
+      const partyHandler = this.scene.ui.getHandler() as PartyUiHandler;
+
+      partyHandler.setCursor(slot);
+      partyHandler.processInput(Button.ACTION); // select party slot
+      partyHandler.processInput(Button.ACTION); // send out (or whatever option is at the top)
+    });
+  }
 }

src/test/utils/phaseInterceptor.ts

@@ -42,7 +42,7 @@ import { QuietFormChangePhase } from "#app/form-change-phase";
 export default class PhaseInterceptor {
   public scene;
   public phases = {};
-  public log;
+  public log: string[];
   private onHold;
   private interval;
   private promptInterval;
@@ -104,13 +104,20 @@ export default class PhaseInterceptor {
    */
   constructor(scene) {
     this.scene = scene;
-    this.log = [];
     this.onHold = [];
     this.prompts = [];
+    this.clearLogs();
     this.startPromptHandler();
     this.initPhases();
   }
 
+  /**
+   * Clears phase logs
+   */
+  clearLogs() {
+    this.log = [];
+  }
+
   rejectAll(error) {
     if (this.inProgress) {
       clearInterval(this.promptInterval);

src/ui/party-ui-handler.ts

@@ -1,13 +1,13 @@
 import { CommandPhase, SelectModifierPhase } from "../phases";
 import BattleScene from "../battle-scene";
-import { PlayerPokemon, PokemonMove } from "../field/pokemon";
+import { MoveResult, PlayerPokemon, PokemonMove } from "../field/pokemon";
 import { addBBCodeTextObject, addTextObject, getTextColor, TextStyle } from "./text";
 import { Command } from "./command-ui-handler";
 import MessageUiHandler from "./message-ui-handler";
 import { Mode } from "./ui";
 import * as Utils from "../utils";
 import { PokemonBaseStatModifier, PokemonFormChangeItemModifier, PokemonHeldItemModifier, SwitchEffectTransferModifier } from "../modifier/modifier";
-import { allMoves } from "../data/move";
+import { allMoves, ForceSwitchOutAttr } from "../data/move";
 import { getGenderColor, getGenderSymbol } from "../data/gender";
 import { StatusEffect } from "../data/status-effect";
 import PokemonIconAnimHandler, { PokemonIconAnimMode } from "./pokemon-icon-anim-handler";
@@ -25,18 +25,69 @@ import { getPokemonNameWithAffix } from "#app/messages.js";
 
 const defaultMessage = i18next.t("partyUiHandler:choosePokemon");
 
+/**
+ * Indicates the reason why the party UI is being opened.
+ */
 export enum PartyUiMode {
+  /**
+   * Indicates that the party UI is open because of a user-opted switch.  This
+   * type of switch can be cancelled.
+   */
   SWITCH,
+  /**
+   * Indicates that the party UI is open because of a faint or other forced
+   * switch (eg, move effect). This type of switch cannot be cancelled.
+   */
   FAINT_SWITCH,
+  /**
+   * Indicates that the party UI is open because of a start-of-encounter optional
+   * switch. This type of switch can be cancelled.
+   */
   POST_BATTLE_SWITCH,
+  /**
+   * Indicates that the party UI is open because of the move Revival Blessing.
+   * This selection cannot be cancelled.
+   */
   REVIVAL_BLESSING,
+  /**
+   * Indicates that the party UI is open to select a mon to apply a modifier to.
+   * This type of selection can be cancelled.
+   */
   MODIFIER,
+  /**
+   * Indicates that the party UI is open to select a mon to apply a move
+   * modifier to (such as an Ether or PP Up).  This type of selection can be cancelled.
+   */
   MOVE_MODIFIER,
+  /**
+   * Indicates that the party UI is open to select a mon to teach a TM.  This
+   * type of selection can be cancelled.
+   */
   TM_MODIFIER,
+  /**
+   * Indicates that the party UI is open to select a mon to remember a move.
+   * This type of selection can be cancelled.
+   */
   REMEMBER_MOVE_MODIFIER,
+  /**
+   * Indicates that the party UI is open to transfer items between mons.  This
+   * type of selection can be cancelled.
+   */
   MODIFIER_TRANSFER,
+  /**
+   * Indicates that the party UI is open because of a DNA Splicer.  This
+   * type of selection can be cancelled.
+   */
   SPLICE,
+  /**
+   * Indicates that the party UI is open to release a party member.  This
+   * type of selection can be cancelled.
+   */
   RELEASE,
+  /**
+   * Indicates that the party UI is open to check the team.  This
+   * type of selection can be cancelled.
+   */
   CHECK
 }
 
@@ -767,10 +818,21 @@ export default class PartyUiHandler extends MessageUiHandler {
       case PartyUiMode.FAINT_SWITCH:
       case PartyUiMode.POST_BATTLE_SWITCH:
         if (this.cursor >= this.scene.currentBattle.getBattlerCount()) {
-          this.options.push(PartyOption.SEND_OUT);
+          const allowBatonModifierSwitch =
-          if (this.partyUiMode !== PartyUiMode.FAINT_SWITCH
+            this.partyUiMode !== PartyUiMode.FAINT_SWITCH
               && this.scene.findModifier(m => m instanceof SwitchEffectTransferModifier
-                  && (m as SwitchEffectTransferModifier).pokemonId === this.scene.getPlayerField()[this.fieldIndex].id)) {
+              && (m as SwitchEffectTransferModifier).pokemonId === this.scene.getPlayerField()[this.fieldIndex].id);
+
+          const moveHistory = this.scene.getPlayerField()[this.fieldIndex].getMoveHistory();
+          const isBatonPassMove = this.partyUiMode === PartyUiMode.FAINT_SWITCH && moveHistory.length && allMoves[moveHistory[moveHistory.length - 1].move].getAttrs(ForceSwitchOutAttr)[0]?.isBatonPass() && moveHistory[moveHistory.length - 1].result === MoveResult.SUCCESS;
+
+          // isBatonPassMove and allowBatonModifierSwitch shouldn't ever be true
+          // at the same time, because they both explicitly check for a mutually
+          // exclusive partyUiMode. But better safe than sorry.
+          this.options.push(isBatonPassMove && !allowBatonModifierSwitch ? PartyOption.PASS_BATON : PartyOption.SEND_OUT);
+          if (allowBatonModifierSwitch && !isBatonPassMove) {
+            // the BATON modifier gives an extra switch option for
+            // pokemon-command switches, allowing buffs to be optionally passed
             this.options.push(PartyOption.PASS_BATON);
           }
         }