From 2fb242d04156fdabe91a5bf94471e5f89cba626c Mon Sep 17 00:00:00 2001
From: Alex <93446519+AlexOn1ine@users.noreply.github.com>
Date: Sun, 8 Mar 2026 20:40:07 +0100
Subject: [PATCH] Fixes Knock Off / Ogerpon behavior (#9478)

---
 src/battle_util.c                   | 10 +++--
 test/battle/move_effect/knock_off.c | 70 +++++++++++++++++++++++++++++
 2 files changed, 77 insertions(+), 3 deletions(-)

diff --git a/src/battle_util.c b/src/battle_util.c
index 1013960fab..23d650da64 100644
--- a/src/battle_util.c
+++ b/src/battle_util.c
@@ -8843,19 +8843,23 @@ bool32 DoBattlersShareType(enum BattlerId battler1, enum BattlerId battler2)
 
 bool32 CanBattlerGetOrLoseItem(enum BattlerId fromBattler, enum BattlerId battler, enum Item itemId)
 {
-    u16 species = gBattleMons[fromBattler].species;
+    u32 fromSpecies = gBattleMons[fromBattler].species;
+    u32 otherSpecies = gBattleMons[battler].species;
+
     enum HoldEffect holdEffect = GetItemHoldEffect(itemId); // Raw hold effect
 
     if (ItemIsMail(itemId))
         return FALSE;
     else if (itemId == ITEM_ENIGMA_BERRY_E_READER)
         return FALSE;
-    else if (DoesSpeciesUseHoldItemToChangeForm(species, itemId))
+    else if (DoesSpeciesUseHoldItemToChangeForm(fromSpecies, itemId))
         return FALSE;
     else if (holdEffect == HOLD_EFFECT_Z_CRYSTAL)
         return FALSE;
     else if (holdEffect == HOLD_EFFECT_BOOSTER_ENERGY
-         && (gSpeciesInfo[gBattleMons[fromBattler].species].isParadox || gSpeciesInfo[gBattleMons[battler].species].isParadox))
+         && (gSpeciesInfo[fromSpecies].isParadox || gSpeciesInfo[otherSpecies].isParadox))
+        return FALSE;
+    else if (holdEffect == HOLD_EFFECT_OGERPON_MASK && GET_BASE_SPECIES_ID(fromSpecies) == SPECIES_OGERPON)
         return FALSE;
     else
         return TRUE;
diff --git a/test/battle/move_effect/knock_off.c b/test/battle/move_effect/knock_off.c
index 8e46ee3151..f8b3f21037 100644
--- a/test/battle/move_effect/knock_off.c
+++ b/test/battle/move_effect/knock_off.c
@@ -437,3 +437,73 @@ SINGLE_BATTLE_TEST("Knock Off does not activate if the item was previously consu
         EXPECT(opponent->item == ITEM_NONE);
     }
 }
+
+SINGLE_BATTLE_TEST("Knock Off does knock off Ogerpon masks from Pokemon that aren't Ogerpon")
+{
+    GIVEN {
+        PLAYER(SPECIES_WOBBUFFET);
+        OPPONENT(SPECIES_WOBBUFFET) { Item(ITEM_HEARTHFLAME_MASK); }
+    } WHEN {
+        TURN { MOVE(opponent, MOVE_CELEBRATE); MOVE(player, MOVE_KNOCK_OFF); }
+    } SCENE {
+        MESSAGE("Wobbuffet knocked off the opposing Wobbuffet's Hearthflame Mask!");
+    } THEN {
+        EXPECT(opponent->item == ITEM_NONE);
+    }
+}
+
+SINGLE_BATTLE_TEST("Knock Off doesn't knock off Ogerpon masks from Ogerpon")
+{
+    GIVEN {
+        PLAYER(SPECIES_WOBBUFFET);
+        OPPONENT(SPECIES_OGERPON) { Item(ITEM_HEARTHFLAME_MASK); }
+    } WHEN {
+        TURN { MOVE(opponent, MOVE_CELEBRATE); MOVE(player, MOVE_KNOCK_OFF); }
+    } SCENE {
+        NOT MESSAGE("Wobbuffet knocked off the opposing Ogerpon's Hearthflame Mask!");
+    } THEN {
+        EXPECT(opponent->item == ITEM_HEARTHFLAME_MASK);
+    }
+}
+
+SINGLE_BATTLE_TEST("Knock Off does knock off a Booster Energy from a non Paradox Pokemon")
+{
+    GIVEN {
+        PLAYER(SPECIES_WOBBUFFET);
+        OPPONENT(SPECIES_WOBBUFFET) { Item(ITEM_BOOSTER_ENERGY); }
+    } WHEN {
+        TURN { MOVE(opponent, MOVE_CELEBRATE); MOVE(player, MOVE_KNOCK_OFF); }
+    } SCENE {
+        MESSAGE("Wobbuffet knocked off the opposing Wobbuffet's Booster Energy!");
+    } THEN {
+        EXPECT(opponent->item == ITEM_NONE);
+    }
+}
+
+SINGLE_BATTLE_TEST("Knock Off doesn't knock off a Paradox mon's Booster Energy")
+{
+    GIVEN {
+        PLAYER(SPECIES_TORKOAL) { Ability(ABILITY_DROUGHT); }
+        OPPONENT(SPECIES_GREAT_TUSK) { Item(ITEM_BOOSTER_ENERGY); }
+    } WHEN {
+        TURN { MOVE(opponent, MOVE_CELEBRATE); MOVE(player, MOVE_KNOCK_OFF); }
+    } SCENE {
+        NOT MESSAGE("Wobbuffet knocked off the opposing Great Tusk's Booster Energy!");
+    } THEN {
+        EXPECT(opponent->item == ITEM_BOOSTER_ENERGY);
+    }
+}
+
+SINGLE_BATTLE_TEST("Knock Off used by a Paradox mon doesn't knock off a non-Paradox mon's Booster Energy")
+{
+    GIVEN {
+        PLAYER(SPECIES_GREAT_TUSK);
+        OPPONENT(SPECIES_WOBBUFFET) { Item(ITEM_BOOSTER_ENERGY); }
+    } WHEN {
+        TURN { MOVE(opponent, MOVE_CELEBRATE); MOVE(player, MOVE_KNOCK_OFF); }
+    } SCENE {
+        NOT MESSAGE("Great Tust knocked off the opposing Wobbuffet's Booster Energy!");
+    } THEN {
+        EXPECT(opponent->item == ITEM_BOOSTER_ENERGY);
+    }
+}