functional but not perfect implementation

data/battle_scripts_1.s

@@ -9560,3 +9560,9 @@ BattleScript_MagicianActivates::
 	call BattleScript_AbilityPopUp
 	call BattleScript_ItemSteal
 	return
+
+BattleScript_SymbiosisActivates::
+	call BattleScript_AbilityPopUp
+	printstring STRINGID_SYMBIOSISITEMPASS
+	waitmessage B_WAIT_TIME_LONG
+	return

include/battle_scripts.h

@@ -419,5 +419,6 @@ extern const u8 BattleScript_MagicianActivates[];
 extern const u8 BattleScript_BeakBlastSetUp[];
 extern const u8 BattleScript_BeakBlastBurn[];
 extern const u8 BattleScript_DefDownSpeedUp[];
+extern const u8 BattleScript_SymbiosisActivates[];
 
 #endif // GUARD_BATTLE_SCRIPTS_H

src/battle_message.c

@@ -601,7 +601,7 @@ static const u8 sText_HarvestBerry[] = _("{B_ATK_NAME_WITH_PREFIX} harvested\nit
 static const u8 sText_LastAbilityRaisedBuff1[] = _("{B_ATK_NAME_WITH_PREFIX}'s {B_LAST_ABILITY}\nraised its {B_BUFF1}!");
 static const u8 sText_MagicBounceActivates[] = _("The {B_DEF_NAME_WITH_PREFIX} bounced the\n{B_ATK_NAME_WITH_PREFIX} back!");
 static const u8 sText_ProteanTypeChange[] = _("{B_ATK_NAME_WITH_PREFIX}'s {B_ATK_ABILITY} transformed\nit into the {B_BUFF1} type!");
-static const u8 sText_SymbiosisItemPass[] = _("{B_ATK_NAME_WITH_PREFIX} passed its {B_LAST_ITEM}\nto {B_SCR_ACTIVE_NAME_WITH_PREFIX} through {B_ATK_ABILITY}!");
+static const u8 sText_SymbiosisItemPass[] = _("{B_SCR_ACTIVE_NAME_WITH_PREFIX} passed its {B_LAST_ITEM}\nto {B_DEF_NAME_WITH_PREFIX} through {B_LAST_ABILITY}!");
 static const u8 sText_StealthRockDmg[] = _("Pointed stones dug into\n{B_SCR_ACTIVE_NAME_WITH_PREFIX}!");
 static const u8 sText_ToxicSpikesAbsorbed[] = _("The poison spikes disappeared\nfrom around the opposing team's feet!");
 static const u8 sText_ToxicSpikesPoisoned[] = _("{B_SCR_ACTIVE_NAME_WITH_PREFIX} was poisoned!");

src/battle_script_commands.c

@@ -7030,6 +7030,53 @@ static bool32 TryCheekPouch(u32 battlerId, u32 itemId)
     return FALSE;
 }
 
+// Notes:
+// Symbiosis applies before a move and after a gem is used in Gen 6.
+// Symbiosis applies if an ally consumes a berry through Bug Bite / Pluck and doesn't have an item.
+// Symbiosis does not apply if an ally has an item stolen, knocked off, or destroyed by Incinerate.
+// Symbiosis does not apply after Eject Button (except in Gen 6, where it is bugged).
+// Symbiosis does not apply if an ally tricks away their item and does not receive one in return.
+
+//itemId is used to check Eject Button or Eject Pack
+static bool32 TrySymbiosis(u32 battler, u32 itemId)
+{
+    u32 ally = battler ^ BIT_FLANK;
+
+    if (!gBattleStruct->itemStolen[gBattlerPartyIndexes[battler]].stolen
+        && gBattleStruct->changedItems[battler] == ITEM_NONE
+        && ItemId_GetHoldEffect(itemId) != HOLD_EFFECT_EJECT_BUTTON
+        && ItemId_GetHoldEffect(itemId) != HOLD_EFFECT_EJECT_PACK
+        && GetBattlerAbility(ally) == ABILITY_SYMBIOSIS
+        && gBattleMons[battler].item == ITEM_NONE
+        && gBattleMons[ally].item != ITEM_NONE
+        && CanBattlerGetOrLoseItem(battler, gBattleMons[ally].item)
+        && CanBattlerGetOrLoseItem(ally, gBattleMons[ally].item)
+        && gBattleMons[battler].hp != 0
+        && gBattleMons[ally].hp != 0)
+    {
+        gLastUsedItem = gBattleMons[ally].item;
+
+        gActiveBattler = ally;
+        gBattleMons[ally].item = ITEM_NONE;
+        BtlController_EmitSetMonData(BUFFER_A, REQUEST_HELDITEM_BATTLE, 0, sizeof(gBattleMons[battler].item), &gBattleMons[battler].item);
+        MarkBattlerForControllerExec(ally);
+
+        gActiveBattler = battler;
+        gBattleMons[battler].item = gLastUsedItem;
+        BtlController_EmitSetMonData(BUFFER_A, REQUEST_HELDITEM_BATTLE, 0, sizeof(gBattleMons[battler].item), &gBattleMons[battler].item);
+        MarkBattlerForControllerExec(battler);
+        gBattleResources->flags->flags[battler] &= ~RESOURCE_FLAG_UNBURDEN;
+
+        gLastUsedAbility = gBattleMons[ally].ability;
+        gBattleScripting.battler = gBattlerAbility = ally;
+        gBattlerTarget = battler;
+        BattleScriptPush(gBattlescriptCurrInstr + 2);
+        gBattlescriptCurrInstr = BattleScript_SymbiosisActivates;
+        return TRUE;
+    }
+    return FALSE;
+}
+
 static void Cmd_removeitem(void)
 {
     u16 itemId = 0;
@@ -7048,7 +7095,7 @@ static void Cmd_removeitem(void)
     MarkBattlerForControllerExec(gActiveBattler);
 
     ClearBattlerItemEffectHistory(gActiveBattler);
-    if (!TryCheekPouch(gActiveBattler, itemId))
+    if (!TryCheekPouch(gActiveBattler, itemId) && !TrySymbiosis(gActiveBattler, itemId))
         gBattlescriptCurrInstr += 2;
 }
 
@@ -8830,6 +8877,7 @@ static void Cmd_various(void)
             MarkBattlerForControllerExec(gActiveBattler);
             gBattleResources->flags->flags[gBattlerTarget] &= ~RESOURCE_FLAG_UNBURDEN;
 
+            if (!TrySymbiosis(gBattlerAttacker, gLastUsedItem))
                 gBattlescriptCurrInstr += 7;
         }
         return;
@@ -12623,6 +12671,7 @@ static void Cmd_tryswapitems(void) // trick
             else
             {
                 CheckSetUnburden(gBattlerAttacker);
+                
                 gBattleCommunication[MULTISTRING_CHOOSER] = B_MSG_ITEM_SWAP_GIVEN; // attacker's item -> <- nothing
             }
         }