Not sure if I'm happy, but it's over...

src/battle-scene.ts

@@ -2632,10 +2632,9 @@ export default class BattleScene extends SceneBase {
     });
   }
 
-  removePartyMemberModifiers(partyMemberIndex: integer): Promise<void> {
+  removePartyMemberModifiers(partyMemberId: integer): Promise<void> {
     return new Promise(resolve => {
-      const pokemonId = this.getPlayerParty()[partyMemberIndex].id;
+      const modifiersToRemove = this.modifiers.filter(m => m instanceof PokemonHeldItemModifier && (m as PokemonHeldItemModifier).pokemonId === partyMemberId);
-      const modifiersToRemove = this.modifiers.filter(m => m instanceof PokemonHeldItemModifier && (m as PokemonHeldItemModifier).pokemonId === pokemonId);
       for (const m of modifiersToRemove) {
         this.modifiers.splice(this.modifiers.indexOf(m), 1);
       }

src/field/pokemon.ts

@@ -5110,7 +5110,7 @@ export class EnemyPokemon extends Pokemon {
    * @param slotIndex an optional index to place the pokemon in the party
    * @returns the pokemon that was added or null if the pokemon could not be added
    */
-  addToParty(pokeballType: PokeballType, slotIndex: number = -1) {
+  addToParty(pokeballType: PokeballType, slotIndex: number = -1, pokemonReplaced?: number | null) {
     const party = this.scene.getPlayerParty();
     let ret: PlayerPokemon | null = null;
 
@@ -5126,6 +5126,15 @@ export class EnemyPokemon extends Pokemon {
         if (slotIndex === 0) {
           newPokemon.setVisible(false); // Hide if replaced with first pokemon
         }
+
+        if (pokemonReplaced && newPokemon.isAllowedInBattle()) {
+          const modifiersToTransfer = this.scene.findModifiers(m => m instanceof PokemonHeldItemModifier && m.pokemonId === pokemonReplaced, true) as PokemonHeldItemModifier[];
+          const transferResults: Promise<boolean>[] = [];
+          for (const modifier of modifiersToTransfer) {
+            transferResults.push(this.scene.tryTransferHeldItemModifier(modifier, newPokemon, false, modifier.getStackCount(), true, true));
+          }
+          Promise.allSettled(transferResults).then(() => newPokemon.scene.removePartyMemberModifiers(pokemonReplaced));
+        }
         party.splice(slotIndex, 0, newPokemon);
       } else {
         party.push(newPokemon);

src/phases/attempt-capture-phase.ts

@@ -233,8 +233,8 @@ export class AttemptCapturePhase extends PokemonPhase {
         this.scene.clearEnemyHeldItemModifiers();
         this.scene.field.remove(pokemon, true);
       };
-      const addToParty = (slotIndex?: number) => {
+      const addToParty = (slotIndex?: number, releasedPokemon?: number) => {
-        const newPokemon = pokemon.addToParty(this.pokeballType, slotIndex);
+        const newPokemon = pokemon.addToParty(this.pokeballType, slotIndex, releasedPokemon);
         const modifiers = this.scene.findModifiers(m => m instanceof PokemonHeldItemModifier, false);
         if (this.scene.getPlayerParty().filter(p => p.isShiny()).length === PLAYER_PARTY_MAX_SIZE) {
           this.scene.validateAchv(achvs.SHINY_PARTY);
@@ -262,15 +262,15 @@ export class AttemptCapturePhase extends PokemonPhase {
                   });
                 }, false);
               }, () => {
-                this.scene.ui.setMode(Mode.PARTY, PartyUiMode.RELEASE, this.fieldIndex, (slotIndex: integer, _option: PartyOption) => {
+                this.scene.ui.setMode(Mode.PARTY, PartyUiMode.RELEASE, this.fieldIndex, (slotIndex: number, _option: PartyOption, releasedPokemon: number) => {
                   this.scene.ui.setMode(Mode.MESSAGE).then(() => {
                     if (slotIndex < 6) {
-                      addToParty(slotIndex);
+                      addToParty(slotIndex, releasedPokemon);
                     } else {
                       promptRelease();
                     }
                   });
-                });
+                }, );
               }, () => {
                 this.scene.ui.setMode(Mode.MESSAGE).then(() => {
                   removePokemon();

src/test/moves/dragon_rage.test.ts

@@ -51,8 +51,6 @@ describe("Moves - Dragon Rage", () => {
     partyPokemon = game.scene.getPlayerParty()[0];
     enemyPokemon = game.scene.getEnemyPokemon()!;
 
-    // remove berries
-    game.scene.removePartyMemberModifiers(0);
     game.scene.clearEnemyHeldItemModifiers();
   });
 

src/test/moves/fissure.test.ts

@@ -46,8 +46,6 @@ describe("Moves - Fissure", () => {
     partyPokemon = game.scene.getPlayerParty()[0];
     enemyPokemon = game.scene.getEnemyPokemon()!;
 
-    // remove berries
-    game.scene.removePartyMemberModifiers(0);
     game.scene.clearEnemyHeldItemModifiers();
   });
 

src/ui/party-ui-handler.ts

@@ -123,7 +123,7 @@ export enum PartyOption {
   ALL = 4000,
 }
 
-export type PartySelectCallback = (cursor: integer, option: PartyOption) => void;
+export type PartySelectCallback = (cursor: integer, option: PartyOption, args?: any | undefined) => void;
 export type PartyModifierTransferSelectCallback = (fromCursor: integer, index: integer, itemQuantity?: integer, toCursor?: integer) => void;
 export type PartyModifierSpliceSelectCallback = (fromCursor: integer, toCursor?: integer) => void;
 export type PokemonSelectFilter = (pokemon: PlayerPokemon) => string | null;
@@ -1061,9 +1061,11 @@ export default class PartyUiHandler extends MessageUiHandler {
   doRelease(slotIndex: integer): void {
     this.showText(this.getReleaseMessage(getPokemonNameWithAffix(this.scene.getPlayerParty()[slotIndex])), null, () => {
       this.clearPartySlots();
-      this.scene.removePartyMemberModifiers(slotIndex);
       const releasedPokemon = this.scene.getPlayerParty().splice(slotIndex, 1)[0];
-      releasedPokemon.destroy();
+      let releasedId: number = 0;
+      if (releasedPokemon.isAllowedInBattle()) {
+        releasedId = releasedPokemon.id;
+      }
       this.populatePartySlots();
       if (this.cursor >= this.scene.getPlayerParty().length) {
         this.setCursor(this.cursor - 1);
@@ -1071,8 +1073,9 @@ export default class PartyUiHandler extends MessageUiHandler {
       if (this.partyUiMode === PartyUiMode.RELEASE) {
         const selectCallback = this.selectCallback;
         this.selectCallback = null;
-        selectCallback && selectCallback(this.cursor, PartyOption.RELEASE);
+        selectCallback && selectCallback(this.cursor, PartyOption.RELEASE, releasedId);
       }
+      releasedPokemon.destroy();
       this.showText("", 0);
     }, null, true);
   }