Multiple refactors

- Added a general GetBattleFormChangeTargetSpecies instead of getting specific ones for Mega Evolution and Primal Reversion.
- Added FORM_CHANGE_BATTLE_HP_PERCENT, to replace ShouldChangeFormHpBased.
- Cleaned ifdefs for hold effects.
- Finally removed UndoMegaEvolution.
- FORM_CHANGE_FAINT and FORM_CHANGE_BATTLE_END restore to the first form before a battle form change if species isn't specified.
- When changing from a form with more HP to one with less, now current HP is kept to fix Zygarde edge case. (Will likely need to be reworked for Dynamax, as it behaves differently)
- Uses DoesSpeciesUseHoldItemToChangeForm in CanBattlerGetOrLoseItem.

include/battle_util.h

@@ -144,14 +144,12 @@ u16 CalcTypeEffectivenessMultiplier(u16 move, u8 moveType, u8 battlerAtk, u8 bat
 u16 CalcPartyMonTypeEffectivenessMultiplier(u16 move, u16 speciesDef, u16 abilityDef);
 u16 GetTypeModifier(u8 atkType, u8 defType);
 s32 GetStealthHazardDamage(u8 hazardType, u8 battlerId);
-u16 GetMegaEvolutionSpecies(u16 preEvoSpecies, u16 heldItemId);
+bool32 DoesSpeciesUseHoldItemToChangeForm(u16 species, u16 heldItemId);
-u16 GetPrimalReversionSpecies(u16 preSpecies, u16 heldItemId);
-u16 GetWishMegaEvolutionSpecies(u16 preEvoSpecies, u16 moveId1, u16 moveId2, u16 moveId3, u16 moveId4);
 bool32 CanMegaEvolve(u8 battlerId);
-void UndoMegaEvolution(u32 monId);
 bool32 IsBattlerMegaEvolved(u8 battlerId);
 bool32 IsBattlerPrimalReverted(u8 battlerId);
-void TryBattleFormChange(u8 battlerId, u16 method);
+u16 GetBattleFormChangeTargetSpecies(u8 battlerId, u16 method);
+bool32 TryBattleFormChange(u8 battlerId, u16 method);
 bool32 DoBattlersShareType(u32 battler1, u32 battler2);
 bool32 CanBattlerGetOrLoseItem(u8 battlerId, u16 itemId);
 struct Pokemon *GetIllusionMonPtr(u32 battlerId);

include/constants/pokemon.h

@@ -323,9 +323,14 @@
 #define FORM_CHANGE_BATTLE_BEGIN        6
 #define FORM_CHANGE_BATTLE_END          7
 #define FORM_CHANGE_BATTLE_SWITCH       8
-#define FORM_CHANGE_MEGA_EVOLUTION_ITEM 9
+#define FORM_CHANGE_BATTLE_HP_PERCENT   9
-#define FORM_CHANGE_MEGA_EVOLUTION_MOVE 10
+#define FORM_CHANGE_MEGA_EVOLUTION_ITEM 10
-#define FORM_CHANGE_PRIMAL_REVERSION    11
+#define FORM_CHANGE_MEGA_EVOLUTION_MOVE 11
+#define FORM_CHANGE_PRIMAL_REVERSION    12
+
+// FORM_CHANGE_BATTLE_HP_PERCENT param2 arguments
+#define HP_HIGHER_THAN      1
+#define HP_LOWER_EQ_THAN    2
 
 #define MON_PIC_WIDTH 64
 #define MON_PIC_HEIGHT 64

include/pokemon.h

@@ -562,7 +562,8 @@ u8 *MonSpritesGfxManager_GetSpritePtr(u8 managerId, u8 spriteNum);
 u16 GetFormSpeciesId(u16 speciesId, u8 formId);
 u8 GetFormIdFromFormSpeciesId(u16 formSpeciesId);
 u16 GetFormChangeTargetSpecies(struct Pokemon *mon, u16 method, u32 arg);
-u16 GetFormChangeTargetSpeciesBoxMon(struct BoxPokemon *mon, u16 method, u32 arg);
+u16 GetFormChangeTargetSpeciesBoxMon(struct BoxPokemon *boxMon, u16 method, u32 arg);
+bool32 DoesSpeciesHaveFormChangeMethod(u16 species, u16 method);
 u16 MonTryLearningNewMoveEvolution(struct Pokemon *mon, bool8 firstMove);
 bool32 ShouldShowFemaleDifferences(u16 species, u32 personality);
 bool32 TryFormChange(u32 monId, u32 side, u16 method);

src/battle_ai_main.c

@@ -3043,12 +3043,8 @@ static bool32 IsPinchBerryItemEffect(u16 holdEffect)
     case HOLD_EFFECT_SP_DEFENSE_UP:
     case HOLD_EFFECT_CRITICAL_UP:
     case HOLD_EFFECT_RANDOM_STAT_UP:
-    #ifdef HOLD_EFFECT_CUSTAP_BERRY
     case HOLD_EFFECT_CUSTAP_BERRY:
-    #endif
-    #ifdef HOLD_EFFECT_MICLE_BERRY
     case HOLD_EFFECT_MICLE_BERRY:
-    #endif
         return TRUE;
     }
 

src/battle_main.c

@@ -3248,8 +3248,6 @@ void FaintClearSetData(void)
 
     Ai_UpdateFaintData(gActiveBattler);
     TryBattleFormChange(gActiveBattler, FORM_CHANGE_FAINT);
-    if (GetBattlerSide(gActiveBattler) == B_SIDE_PLAYER)
-        UndoMegaEvolution(gBattlerPartyIndexes[gActiveBattler]);
 
     gBattleStruct->overwrittenAbilities[gActiveBattler] = ABILITY_NONE;
 
@@ -3683,7 +3681,7 @@ static void TryDoEventsBeforeFirstTurn(void)
     for (i = 0; i < gBattlersCount; i++)
     {
         if (GetBattlerHoldEffect(i, TRUE) == HOLD_EFFECT_PRIMAL_ORB
-            && GetPrimalReversionSpecies(gBattleMons[i].species, gBattleMons[i].item) != SPECIES_NONE)
+            && GetBattleFormChangeTargetSpecies(i, FORM_CHANGE_PRIMAL_REVERSION) != SPECIES_NONE)
         {
             gBattlerAttacker = i;
             BattleScriptExecute(BattleScript_PrimalReversion);
@@ -5200,16 +5198,15 @@ static void HandleEndTurn_FinishBattle(void)
     #endif
         for (i = 0; i < PARTY_SIZE; i++)
         {
-            UndoMegaEvolution(i);
+            bool32 changedForm = TryFormChange(i, B_SIDE_PLAYER, FORM_CHANGE_BATTLE_END);
-            TryFormChange(i, B_SIDE_PLAYER, FORM_CHANGE_BATTLE_END);
             DoBurmyFormChange(i);
+            // Clear original species field
+            gBattleStruct->changedSpecies[i] = SPECIES_NONE;
+
         #if B_RECALCULATE_STATS >= GEN_5
             // Recalculate the stats of every party member before the end
-            if (GetMonData(&gPlayerParty[i], MON_DATA_SPECIES2) != SPECIES_NONE
+            if (!changedForm)
-             && GetMonData(&gPlayerParty[i], MON_DATA_SPECIES2) != SPECIES_EGG)
-            {
                 CalculateMonStats(&gPlayerParty[i]);
-            }
         #endif
         }
         // Clear battle mon species to avoid a bug on the next battle that causes

src/battle_script_commands.c

@@ -8800,10 +8800,10 @@ static void Cmd_various(void)
         if (gBattlescriptCurrInstr[3] == 0)
         {
             //Checks regular Mega Evolution
-            u16 megaSpecies = GetMegaEvolutionSpecies(gBattleMons[gActiveBattler].species, gBattleMons[gActiveBattler].item);
+            u16 megaSpecies = GetBattleFormChangeTargetSpecies(gActiveBattler, FORM_CHANGE_MEGA_EVOLUTION_ITEM);
             //Checks Wish Mega Evolution
             if (megaSpecies == SPECIES_NONE)
-                megaSpecies = GetWishMegaEvolutionSpecies(gBattleMons[gActiveBattler].species, gBattleMons[gActiveBattler].moves[0], gBattleMons[gActiveBattler].moves[1], gBattleMons[gActiveBattler].moves[2], gBattleMons[gActiveBattler].moves[3]);
+                megaSpecies = GetBattleFormChangeTargetSpecies(gActiveBattler, FORM_CHANGE_MEGA_EVOLUTION_MOVE);
 
             gBattleMons[gActiveBattler].species = megaSpecies;
             PREPARE_SPECIES_BUFFER(gBattleTextBuff1, gBattleMons[gActiveBattler].species);
@@ -8836,7 +8836,7 @@ static void Cmd_various(void)
         // Change species.
         if (gBattlescriptCurrInstr[3] == 0)
         {
-            gBattleMons[gActiveBattler].species = GetPrimalReversionSpecies(gBattleMons[gActiveBattler].species, gBattleMons[gActiveBattler].item);
+            gBattleMons[gActiveBattler].species = GetBattleFormChangeTargetSpecies(gActiveBattler, FORM_CHANGE_PRIMAL_REVERSION);
             PREPARE_SPECIES_BUFFER(gBattleTextBuff1, gBattleMons[gActiveBattler].species);
 
             BtlController_EmitSetMonData(BUFFER_A, REQUEST_SPECIES_BATTLE, gBitTable[gBattlerPartyIndexes[gActiveBattler]], sizeof(gBattleMons[gActiveBattler].species), &gBattleMons[gActiveBattler].species);
@@ -9561,7 +9561,7 @@ static void Cmd_various(void)
         return;
     case VARIOUS_JUMP_IF_CANT_REVERT_TO_PRIMAL:
     {
-        if (GetPrimalReversionSpecies(gBattleMons[gActiveBattler].species, gBattleMons[gActiveBattler].item) == SPECIES_NONE)
+        if (GetBattleFormChangeTargetSpecies(gActiveBattler, FORM_CHANGE_PRIMAL_REVERSION) == SPECIES_NONE)
             gBattlescriptCurrInstr = T1_READ_PTR(gBattlescriptCurrInstr + 3);
         else
             gBattlescriptCurrInstr += 7;

src/battle_util.c

@@ -4170,51 +4170,6 @@ static bool32 TryChangeBattleTerrain(u32 battler, u32 statusFlag, u8 *timer)
     return FALSE;
 }
 
-static bool32 ShouldChangeFormHpBased(u32 battler)
-{
-    // Ability,     form >, form <=, hp divided
-    static const u16 forms[][4] =
-    {
-        {ABILITY_ZEN_MODE, SPECIES_DARMANITAN, SPECIES_DARMANITAN_ZEN_MODE, 2},
-        {ABILITY_SHIELDS_DOWN, SPECIES_MINIOR, SPECIES_MINIOR_CORE_RED, 2},
-        {ABILITY_SHIELDS_DOWN, SPECIES_MINIOR_METEOR_BLUE, SPECIES_MINIOR_CORE_BLUE, 2},
-        {ABILITY_SHIELDS_DOWN, SPECIES_MINIOR_METEOR_GREEN, SPECIES_MINIOR_CORE_GREEN, 2},
-        {ABILITY_SHIELDS_DOWN, SPECIES_MINIOR_METEOR_INDIGO, SPECIES_MINIOR_CORE_INDIGO, 2},
-        {ABILITY_SHIELDS_DOWN, SPECIES_MINIOR_METEOR_ORANGE, SPECIES_MINIOR_CORE_ORANGE, 2},
-        {ABILITY_SHIELDS_DOWN, SPECIES_MINIOR_METEOR_VIOLET, SPECIES_MINIOR_CORE_VIOLET, 2},
-        {ABILITY_SHIELDS_DOWN, SPECIES_MINIOR_METEOR_YELLOW, SPECIES_MINIOR_CORE_YELLOW, 2},
-        {ABILITY_SCHOOLING, SPECIES_WISHIWASHI_SCHOOL, SPECIES_WISHIWASHI, 4},
-        {ABILITY_GULP_MISSILE, SPECIES_CRAMORANT, SPECIES_CRAMORANT_GORGING, 2},
-        {ABILITY_GULP_MISSILE, SPECIES_CRAMORANT, SPECIES_CRAMORANT_GULPING, 1},
-        {ABILITY_ZEN_MODE, SPECIES_DARMANITAN_GALARIAN, SPECIES_DARMANITAN_ZEN_MODE_GALARIAN, 2},
-    };
-    u32 i;
-    u16 battlerAbility = GetBattlerAbility(battler);
-
-    if (gBattleMons[battler].status2 & STATUS2_TRANSFORMED)
-        return FALSE;
-
-    for (i = 0; i < ARRAY_COUNT(forms); i++)
-    {
-        if (battlerAbility == forms[i][0])
-        {
-            if (gBattleMons[battler].species == forms[i][2]
-                && gBattleMons[battler].hp > gBattleMons[battler].maxHP / forms[i][3])
-            {
-                gBattleMons[battler].species = forms[i][1];
-                return TRUE;
-            }
-            if (gBattleMons[battler].species == forms[i][1]
-                && gBattleMons[battler].hp <= gBattleMons[battler].maxHP / forms[i][3])
-            {
-                gBattleMons[battler].species = forms[i][2];
-                return TRUE;
-            }
-        }
-    }
-    return FALSE;
-}
-
 static u8 ForewarnChooseMove(u32 battler)
 {
     struct Forewarn {
@@ -4738,7 +4693,7 @@ u8 AbilityBattleEffects(u8 caseID, u8 battler, u16 ability, u8 special, u16 move
         // Fallthrough
         case ABILITY_ZEN_MODE:
         case ABILITY_SHIELDS_DOWN:
-            if (ShouldChangeFormHpBased(battler))
+            if (TryBattleFormChange(battler, FORM_CHANGE_BATTLE_HP_PERCENT))
             {
                 BattleScriptPushCursorAndCallback(BattleScript_AttackerFormChangeEnd3);
                 effect++;
@@ -4959,15 +4914,9 @@ u8 AbilityBattleEffects(u8 caseID, u8 battler, u16 ability, u8 special, u16 move
             // Fallthrough
             case ABILITY_ZEN_MODE:
             case ABILITY_SHIELDS_DOWN:
-                if ((effect = ShouldChangeFormHpBased(battler)))
-                    BattleScriptPushCursorAndCallback(BattleScript_AttackerFormChangeEnd3);
-                break;
             case ABILITY_POWER_CONSTRUCT:
-                if ((gBattleMons[battler].species == SPECIES_ZYGARDE || gBattleMons[battler].species == SPECIES_ZYGARDE_10)
+                if (TryBattleFormChange(battler, FORM_CHANGE_BATTLE_HP_PERCENT))
-                    && gBattleMons[battler].hp <= gBattleMons[battler].maxHP / 2)
                 {
-                    gBattleStruct->changedSpecies[gBattlerPartyIndexes[battler]] = gBattleMons[battler].species;
-                    gBattleMons[battler].species = SPECIES_ZYGARDE_COMPLETE;
                     BattleScriptPushCursorAndCallback(BattleScript_AttackerFormChangeEnd3);
                     effect++;
                 }
@@ -5614,7 +5563,6 @@ u8 AbilityBattleEffects(u8 caseID, u8 battler, u16 ability, u8 special, u16 move
             {
                 if (gBattleMons[gBattlerTarget].species == SPECIES_CRAMORANT_GORGING)
                 {
-                    gBattleStruct->changedSpecies[gBattlerPartyIndexes[gBattlerTarget]] = gBattleMons[gBattlerTarget].species;
                     gBattleMons[gBattlerTarget].species = SPECIES_CRAMORANT;
                     if (GetBattlerAbility(gBattlerAttacker) != ABILITY_MAGIC_GUARD)
                     {
@@ -5628,7 +5576,6 @@ u8 AbilityBattleEffects(u8 caseID, u8 battler, u16 ability, u8 special, u16 move
                 }
                 else if (gBattleMons[gBattlerTarget].species == SPECIES_CRAMORANT_GULPING)
                 {
-                    gBattleStruct->changedSpecies[gBattlerPartyIndexes[gBattlerTarget]] = gBattleMons[gBattlerTarget].species;
                     gBattleMons[gBattlerTarget].species = SPECIES_CRAMORANT;
                     if (GetBattlerAbility(gBattlerAttacker) != ABILITY_MAGIC_GUARD)
                     {
@@ -5681,7 +5628,7 @@ u8 AbilityBattleEffects(u8 caseID, u8 battler, u16 ability, u8 special, u16 move
             break;
         case ABILITY_GULP_MISSILE:
             if (((gCurrentMove == MOVE_SURF && TARGET_TURN_DAMAGED) || gStatuses3[gBattlerAttacker] & STATUS3_UNDERWATER)
-             && (effect = ShouldChangeFormHpBased(gBattlerAttacker)))
+             && TryBattleFormChange(gBattlerAttacker, FORM_CHANGE_BATTLE_HP_PERCENT))
             {
                 BattleScriptPushCursor();
                 gBattlescriptCurrInstr = BattleScript_AttackerFormChange;
@@ -9552,59 +9499,27 @@ bool32 IsPartnerMonFromSameTrainer(u8 battlerId)
         return TRUE;
 }
 
-u16 GetMegaEvolutionSpecies(u16 preEvoSpecies, u16 heldItemId)
+bool32 DoesSpeciesUseHoldItemToChangeForm(u16 species, u16 heldItemId)
 {
     u32 i;
-    const struct FormChange *formChanges = gFormChangeTablePointers[preEvoSpecies];
+    const struct FormChange *formChanges = gFormChangeTablePointers[species];
 
     if (formChanges != NULL)
     {
         for (i = 0; formChanges[i].method != FORM_CHANGE_END; i++)
         {
-            if ((formChanges[i].method == FORM_CHANGE_MEGA_EVOLUTION_ITEM
+            switch (formChanges[i].method)
-             && formChanges[i].param1 == heldItemId)
-             && formChanges[i].targetSpecies != preEvoSpecies)
-                return formChanges[i].targetSpecies;
-        }
-    }
-    return SPECIES_NONE;
-}
-
-u16 GetPrimalReversionSpecies(u16 preSpecies, u16 heldItemId)
             {
-    u32 i;
+            case FORM_CHANGE_MEGA_EVOLUTION_ITEM:
-    const struct FormChange *formChanges = gFormChangeTablePointers[preSpecies];
+            case FORM_CHANGE_PRIMAL_REVERSION:
-
+            case FORM_CHANGE_ITEM_HOLD:
-    if (formChanges != NULL)
+                if (formChanges[i].param1 == heldItemId)
-    {
+                    return TRUE;
-        for (i = 0; formChanges[i].method != FORM_CHANGE_END; i++)
+                break;
-        {
-            if (formChanges[i].method == FORM_CHANGE_PRIMAL_REVERSION
-             && formChanges[i].param1 == heldItemId
-             && formChanges[i].targetSpecies != preSpecies)
-                return formChanges[i].targetSpecies;
             }
         }
-    return SPECIES_NONE;
     }
-
+    return FALSE;
-u16 GetWishMegaEvolutionSpecies(u16 preEvoSpecies, u16 moveId1, u16 moveId2, u16 moveId3, u16 moveId4)
-{
-    u32 i, param;
-    const struct FormChange *formChanges = gFormChangeTablePointers[preEvoSpecies];
-
-    if (formChanges != NULL)
-    {
-        for (i = 0; formChanges[i].method != FORM_CHANGE_END; i++)
-        {
-            param = formChanges[i].param1;
-            if ((formChanges[i].method == FORM_CHANGE_MEGA_EVOLUTION_MOVE
-             && (param == moveId1 || param == moveId2 || param == moveId3 || param == moveId4))
-             && formChanges[i].targetSpecies != preEvoSpecies)
-                return formChanges[i].targetSpecies;
-        }
-    }
-    return SPECIES_NONE;
 }
 
 bool32 CanMegaEvolve(u8 battlerId)
@@ -9647,7 +9562,7 @@ bool32 CanMegaEvolve(u8 battlerId)
     itemId = GetMonData(mon, MON_DATA_HELD_ITEM);
 
     // Check if there is an entry in the evolution table for regular Mega Evolution.
-    if (GetMegaEvolutionSpecies(species, itemId) != SPECIES_NONE)
+    if (GetBattleFormChangeTargetSpecies(battlerId, FORM_CHANGE_MEGA_EVOLUTION_ITEM) != SPECIES_NONE)
     {
     #if B_ENABLE_DEBUG == TRUE
         if (B_ENABLE_DEBUG && gBattleStruct->debugHoldEffects[battlerId])
@@ -9668,7 +9583,7 @@ bool32 CanMegaEvolve(u8 battlerId)
     }
 
     // Check if there is an entry in the evolution table for Wish Mega Evolution.
-    if (GetWishMegaEvolutionSpecies(species, GetMonData(mon, MON_DATA_MOVE1), GetMonData(mon, MON_DATA_MOVE2), GetMonData(mon, MON_DATA_MOVE3), GetMonData(mon, MON_DATA_MOVE4)))
+    if (GetBattleFormChangeTargetSpecies(battlerId, FORM_CHANGE_MEGA_EVOLUTION_MOVE) != SPECIES_NONE)
     {
         gBattleStruct->mega.isWishMegaEvo = TRUE;
         return TRUE;
@@ -9678,17 +9593,6 @@ bool32 CanMegaEvolve(u8 battlerId)
     return FALSE;
 }
 
-void UndoMegaEvolution(u32 monId)
-{
-    // While not exactly a mega evolution, Zygarde follows the same rules.
-    if (GetMonData(&gPlayerParty[monId], MON_DATA_SPECIES, NULL) == SPECIES_ZYGARDE_COMPLETE)
-    {
-        SetMonData(&gPlayerParty[monId], MON_DATA_SPECIES, &gBattleStruct->changedSpecies[monId]);
-        gBattleStruct->changedSpecies[monId] = 0;
-        CalculateMonStats(&gPlayerParty[monId]);
-    }
-}
-
 bool32 IsBattlerMegaEvolved(u8 battlerId)
 {
     return (gBaseStats[gBattleMons[battlerId].species].flags & SPECIES_FLAG_MEGA_EVOLUTION);
@@ -9699,17 +9603,121 @@ bool32 IsBattlerPrimalReverted(u8 battlerId)
     return (gBaseStats[gBattleMons[battlerId].species].flags & SPECIES_FLAG_PRIMAL_REVERSION);
 }
 
-void TryBattleFormChange(u8 battlerId, u16 method)
+// Returns SPECIES_NONE if no form change is possible
+u16 GetBattleFormChangeTargetSpecies(u8 battlerId, u16 method)
+{
+    u32 i, j;
+    u16 targetSpecies = SPECIES_NONE;
+    u16 species = gBattleMons[battlerId].species;
+    const struct FormChange *formChanges = gFormChangeTablePointers[species];
+    u16 heldItem;
+    u32 ability;
+
+    if (formChanges != NULL)
+    {
+        heldItem = gBattleMons[battlerId].item;
+        ability = GetBattlerAbility(battlerId);
+
+        for (i = 0; formChanges[i].method != FORM_CHANGE_END; i++)
+        {
+            if (method == formChanges[i].method && species != formChanges[i].targetSpecies)
+            {
+                switch (method)
+                {
+                case FORM_CHANGE_MEGA_EVOLUTION_ITEM:
+                case FORM_CHANGE_PRIMAL_REVERSION:
+                    if (heldItem == formChanges[i].param1)
+                        targetSpecies = formChanges[i].targetSpecies;
+                    break;
+                case FORM_CHANGE_MEGA_EVOLUTION_MOVE:
+                    if (gBattleMons[battlerId].moves[0] == formChanges[i].param1
+                     || gBattleMons[battlerId].moves[1] == formChanges[i].param1
+                     || gBattleMons[battlerId].moves[2] == formChanges[i].param1
+                     || gBattleMons[battlerId].moves[3] == formChanges[i].param1)
+                        targetSpecies = formChanges[i].targetSpecies;
+                    break;
+                case FORM_CHANGE_BATTLE_SWITCH:
+                    targetSpecies = formChanges[i].targetSpecies;
+                    break;
+                case FORM_CHANGE_BATTLE_HP_PERCENT:
+                {
+                    if (formChanges[i].param1 == GetBattlerAbility(battlerId))
+                    {
+                        // We multiply by 100 to make sure that integer division doesn't mess with the health check.
+                        u32 hpCheck = gBattleMons[battlerId].hp * 100 * 100 / gBattleMons[battlerId].maxHP;
+                        switch(formChanges[i].param2)
+                        {
+                        case HP_HIGHER_THAN:
+                            if (hpCheck > formChanges[i].param3 * 100)
+                                targetSpecies = formChanges[i].targetSpecies;
+                            break;
+                        case HP_LOWER_EQ_THAN:
+                            if (hpCheck <= formChanges[i].param3 * 100)
+                                targetSpecies = formChanges[i].targetSpecies;
+                            break;
+                        }
+                    }
+                    break;
+                }
+                }
+            }
+        }
+    }
+
+    return targetSpecies;
+}
+
+bool32 TryBattleFormChange(u8 battlerId, u16 method)
 {
     u8 monId = gBattlerPartyIndexes[battlerId];
     u8 side = GET_BATTLER_SIDE(battlerId);
     struct Pokemon *party = (side == B_SIDE_PLAYER) ? gPlayerParty : gEnemyParty;
+    u16 targetSpecies;
 
-    if (TryFormChange(monId, side, method))
+    // Can't change form if transformed.
+    if (gBattleMons[battlerId].status2 & STATUS2_TRANSFORMED)
+        return FALSE;
+
+    if (!DoesSpeciesHaveFormChangeMethod(gBattleMons[battlerId].species, method))
+        return FALSE;
+
+    targetSpecies = GetBattleFormChangeTargetSpecies(battlerId, method);
+    if (targetSpecies != SPECIES_NONE)
     {
-        CopyMonLevelAndBaseStatsToBattleMon(battlerId, &party[monId]);
+        // Saves the original species on the first form change.
-        CopyMonAbilityAndTypesToBattleMon(battlerId, &party[monId]);
+        if (gBattleStruct->changedSpecies[monId] == SPECIES_NONE)
+            gBattleStruct->changedSpecies[monId] = gBattleMons[battlerId].species;
+
+        TryToSetBattleFormChangeMoves(&party[monId], method);
+        SetMonData(&party[monId], MON_DATA_SPECIES, &targetSpecies);
+        gBattleMons[battlerId].species = targetSpecies;
+        RecalcBattlerStats(battlerId, &party[monId]);
+        return TRUE;
     }
+
+    targetSpecies = GetFormChangeTargetSpecies(&party[monId], method, 0);
+    if (targetSpecies != SPECIES_NONE)
+    {
+        // Saves the original species on the first form change.
+        if (gBattleStruct->changedSpecies[monId] == SPECIES_NONE)
+            gBattleStruct->changedSpecies[monId] = targetSpecies;
+
+        TryToSetBattleFormChangeMoves(&party[monId], method);
+        SetMonData(&party[monId], MON_DATA_SPECIES, &targetSpecies);
+        gBattleMons[battlerId].species = targetSpecies;
+        RecalcBattlerStats(battlerId, &party[monId]);
+        return TRUE;
+    }
+    else if ((method == FORM_CHANGE_BATTLE_END || method == FORM_CHANGE_FAINT)
+            && gBattleStruct->changedSpecies[monId] != SPECIES_NONE)
+    {
+        TryToSetBattleFormChangeMoves(&party[monId], method);
+        SetMonData(&party[monId], MON_DATA_SPECIES, &gBattleStruct->changedSpecies[monId]);
+        RecalcBattlerStats(battlerId, &party[monId]);
+        return TRUE;
+    }
+
+    return FALSE;
 }
 
 bool32 DoBattlersShareType(u32 battler1, u32 battler2)
@@ -9740,24 +9748,10 @@ bool32 CanBattlerGetOrLoseItem(u8 battlerId, u16 itemId)
     // Mail can be stolen now
     if (itemId == ITEM_ENIGMA_BERRY_E_READER)
         return FALSE;
-    // Primal Reversion inducing items cannot be lost if pokemon's base species can undergo primal reversion with it.
+    else if (DoesSpeciesUseHoldItemToChangeForm(species, itemId))
-    else if (holdEffect == HOLD_EFFECT_PRIMAL_ORB && (GetPrimalReversionSpecies(GET_BASE_SPECIES_ID(species), itemId) != SPECIES_NONE))
         return FALSE;
-    // Mega stone cannot be lost if pokemon's base species can mega evolve with it.
-    else if (holdEffect == HOLD_EFFECT_MEGA_STONE && (GetMegaEvolutionSpecies(GET_BASE_SPECIES_ID(species), itemId) != SPECIES_NONE))
-        return FALSE;
-    else if (GET_BASE_SPECIES_ID(species) == SPECIES_GIRATINA && itemId == ITEM_GRISEOUS_ORB)
-        return FALSE;
-    else if (GET_BASE_SPECIES_ID(species) == SPECIES_GENESECT && holdEffect == HOLD_EFFECT_DRIVE)
-        return FALSE;
-    else if (GET_BASE_SPECIES_ID(species) == SPECIES_SILVALLY && holdEffect == HOLD_EFFECT_MEMORY)
-        return FALSE;
-    else if (GET_BASE_SPECIES_ID(species) == SPECIES_ARCEUS && holdEffect == HOLD_EFFECT_PLATE)
-        return FALSE;
-#ifdef HOLD_EFFECT_Z_CRYSTAL
     else if (holdEffect == HOLD_EFFECT_Z_CRYSTAL)
         return FALSE;
-#endif
     else
         return TRUE;
 }

src/data/pokemon/form_change_table_pointers.h

@@ -148,6 +148,9 @@ const struct FormChange *const gFormChangeTablePointers[NUM_SPECIES] =
     [SPECIES_AEGISLASH_BLADE] = sAegislashFormChangeTable,
     [SPECIES_XERNEAS] = sXerneasFormChangeTable,
     [SPECIES_XERNEAS_ACTIVE] = sXerneasFormChangeTable,
+    [SPECIES_ZYGARDE_10_POWER_CONSTRUCT] = sZygardePowerConstructFormChangeTable,
+    [SPECIES_ZYGARDE_50_POWER_CONSTRUCT] = sZygardePowerConstructFormChangeTable,
+    [SPECIES_ZYGARDE_COMPLETE] = sZygardePowerConstructFormChangeTable,
     [SPECIES_DIANCIE] = sDiancieFormChangeTable,
     [SPECIES_DIANCIE_MEGA] = sDiancieFormChangeTable,
     [SPECIES_HOOPA] = sHoopaFormChangeTable,

src/data/pokemon/form_change_tables.h

@@ -24,6 +24,8 @@ FORM_CHANGE_WITHDRAW:
 
 FORM_CHANGE_FAINT:
     Form change activates when the Pokémon faints, either in battle or in the overworld by poison.
+    If species is not specified and it's on the player's side, it will try to use the value
+    saved in gBattleStruct->changedSpecies from a previous form change.
     No parameters.
 
 FORM_CHANGE_BATTLE_BEGIN:
@@ -33,7 +35,8 @@ FORM_CHANGE_BATTLE_BEGIN:
     param3 = a new move to replace it with, optional
 
 FORM_CHANGE_BATTLE_END:
-    Form change activates at the end of a battle
+    Form change activates at the end of a battle. If species is not specified and it's on the player's side,
+    it will try to use the value saved in gBattleStruct->changedSpecies from a previous form change.
     param1 = item to hold, optional
     param2 = a move that will be replaced, optional
     param3 = a new move to replace it with, optional
@@ -42,10 +45,27 @@ FORM_CHANGE_BATTLE_SWITCH:
     Form change activates when the Pokémon is switched out in battle.
     No parameters.
 
+FORM_CHANGE_BATTLE_HP_PERCENT:
+    Form change activates when the Pokémon's HP % passes a certain threshold.
+    param1 = Ability to check.
+    param2 = HP_HIGHER_THAN if the form triggers when the current HP is higher than the specified threshold.
+             HP_LOWER_EQ_THAN if the form triggers when the current HP is lower or equal than the specified threshold.
+    param3 = HP percentage threshold.
+
+FORM_CHANGE_MEGA_EVOLUTION_ITEM:
+    Form change activates when the mon has the defined item. If it's on the player's side, it also requires
+    ITEM_MEGA_RING in the user's bag and for the player to choose to enable it.
+    param1 = item to hold.
+
+FORM_CHANGE_MEGA_EVOLUTION_MOVE:
+    Form change activates when the mon has the defined move. If it's on the player's side, it also requires
+    ITEM_MEGA_RING in the user's bag and for the player to choose to enable it.
+    param1 = move to have.
+
 FORM_CHANGE_PRIMAL_REVERSION:
-    Form change activates when entering battle with the specified item. If the item is a Red Orb,
+    Form change activates automatically when entering battle with the specified item. If the item is a Red Orb,
     it uses the Omega Symbol for the animation and icon. Otherwise, it defaults to Alpha.
-    param1 = item to hold, required.
+    param1 = item to hold.
 */
 
 // FORM_CHANGE_MOVE param2 Arguments
@@ -440,14 +460,16 @@ static const struct FormChange sAudinoFormChangeTable[] = {
 };
 
 static const struct FormChange sDarmanitanFormChangeTable[] = {
-    {FORM_CHANGE_BATTLE_SWITCH, SPECIES_DARMANITAN},
+    {FORM_CHANGE_BATTLE_HP_PERCENT, SPECIES_DARMANITAN,          ABILITY_ZEN_MODE, HP_HIGHER_THAN,   50},
+    {FORM_CHANGE_BATTLE_HP_PERCENT, SPECIES_DARMANITAN_ZEN_MODE, ABILITY_ZEN_MODE, HP_LOWER_EQ_THAN, 50},
     {FORM_CHANGE_FAINT,             SPECIES_DARMANITAN},
     {FORM_CHANGE_BATTLE_END,        SPECIES_DARMANITAN},
     {FORM_CHANGE_END},
 };
 
 static const struct FormChange sDarmanitanGalarianFormChangeTable[] = {
-    {FORM_CHANGE_BATTLE_SWITCH, SPECIES_DARMANITAN_GALARIAN},
+    {FORM_CHANGE_BATTLE_HP_PERCENT, SPECIES_DARMANITAN_GALARIAN,          ABILITY_ZEN_MODE, HP_HIGHER_THAN,   50},
+    {FORM_CHANGE_BATTLE_HP_PERCENT, SPECIES_DARMANITAN_ZEN_MODE_GALARIAN, ABILITY_ZEN_MODE, HP_LOWER_EQ_THAN, 50},
     {FORM_CHANGE_FAINT,             SPECIES_DARMANITAN_GALARIAN},
     {FORM_CHANGE_BATTLE_END,        SPECIES_DARMANITAN_GALARIAN},
     {FORM_CHANGE_END},
@@ -513,6 +535,13 @@ static const struct FormChange sXerneasFormChangeTable[] = {
     {FORM_CHANGE_END},
 };
 
+static const struct FormChange sZygardePowerConstructFormChangeTable[] = {
+    {FORM_CHANGE_BATTLE_HP_PERCENT, SPECIES_ZYGARDE_COMPLETE, ABILITY_POWER_CONSTRUCT, HP_LOWER_EQ_THAN, 50},
+    {FORM_CHANGE_FAINT},
+    {FORM_CHANGE_BATTLE_END},
+    {FORM_CHANGE_END},
+};
+
 static const struct FormChange sDiancieFormChangeTable[] = {
     {FORM_CHANGE_MEGA_EVOLUTION_ITEM,   SPECIES_DIANCIE_MEGA, ITEM_DIANCITE},
     {FORM_CHANGE_FAINT,                 SPECIES_DIANCIE},
@@ -536,6 +565,8 @@ static const struct FormChange sOricorioFormChangeTable[] = {
     {FORM_CHANGE_END},
 };
 static const struct FormChange sWishiwashiFormChangeTable[] = {
+    {FORM_CHANGE_BATTLE_HP_PERCENT, SPECIES_WISHIWASHI_SCHOOL, ABILITY_SCHOOLING, HP_HIGHER_THAN,   25},
+    {FORM_CHANGE_BATTLE_HP_PERCENT, SPECIES_WISHIWASHI,        ABILITY_SCHOOLING, HP_LOWER_EQ_THAN, 25},
     {FORM_CHANGE_BATTLE_SWITCH,     SPECIES_WISHIWASHI},
     {FORM_CHANGE_FAINT,             SPECIES_WISHIWASHI},
     {FORM_CHANGE_BATTLE_END,        SPECIES_WISHIWASHI},
@@ -571,52 +602,67 @@ static const struct FormChange sMimikyuFormChangeTable[] = {
 };
 
 static const struct FormChange sMiniorRedFormChangeTable[] = {
+    {FORM_CHANGE_BATTLE_HP_PERCENT, SPECIES_MINIOR,          ABILITY_SHIELDS_DOWN, HP_HIGHER_THAN,   50},
+    {FORM_CHANGE_BATTLE_HP_PERCENT, SPECIES_MINIOR_CORE_RED, ABILITY_SHIELDS_DOWN, HP_LOWER_EQ_THAN, 50},
     {FORM_CHANGE_BATTLE_SWITCH,     SPECIES_MINIOR_CORE_RED},
     {FORM_CHANGE_FAINT,             SPECIES_MINIOR_CORE_RED},
     {FORM_CHANGE_BATTLE_END,        SPECIES_MINIOR_CORE_RED},
     {FORM_CHANGE_END},
 };
 static const struct FormChange sMiniorBlueFormChangeTable[] = {
+    {FORM_CHANGE_BATTLE_HP_PERCENT, SPECIES_MINIOR_METEOR_BLUE, ABILITY_SHIELDS_DOWN, HP_HIGHER_THAN,   50},
+    {FORM_CHANGE_BATTLE_HP_PERCENT, SPECIES_MINIOR_CORE_BLUE,   ABILITY_SHIELDS_DOWN, HP_LOWER_EQ_THAN, 50},
     {FORM_CHANGE_BATTLE_SWITCH,     SPECIES_MINIOR_CORE_BLUE},
     {FORM_CHANGE_FAINT,             SPECIES_MINIOR_CORE_BLUE},
     {FORM_CHANGE_BATTLE_END,        SPECIES_MINIOR_CORE_BLUE},
     {FORM_CHANGE_END},
 };
 static const struct FormChange sMiniorGreenFormChangeTable[] = {
+    {FORM_CHANGE_BATTLE_HP_PERCENT, SPECIES_MINIOR_METEOR_GREEN, ABILITY_SHIELDS_DOWN, HP_HIGHER_THAN,   50},
+    {FORM_CHANGE_BATTLE_HP_PERCENT, SPECIES_MINIOR_CORE_GREEN,   ABILITY_SHIELDS_DOWN, HP_LOWER_EQ_THAN, 50},
     {FORM_CHANGE_BATTLE_SWITCH,     SPECIES_MINIOR_CORE_GREEN},
     {FORM_CHANGE_FAINT,             SPECIES_MINIOR_CORE_GREEN},
     {FORM_CHANGE_BATTLE_END,        SPECIES_MINIOR_CORE_GREEN},
     {FORM_CHANGE_END},
 };
 static const struct FormChange sMiniorIndigoFormChangeTable[] = {
+    {FORM_CHANGE_BATTLE_HP_PERCENT, SPECIES_MINIOR_METEOR_INDIGO, ABILITY_SHIELDS_DOWN, HP_HIGHER_THAN,   50},
+    {FORM_CHANGE_BATTLE_HP_PERCENT, SPECIES_MINIOR_CORE_INDIGO,   ABILITY_SHIELDS_DOWN, HP_LOWER_EQ_THAN, 50},
     {FORM_CHANGE_BATTLE_SWITCH,     SPECIES_MINIOR_CORE_INDIGO},
     {FORM_CHANGE_FAINT,             SPECIES_MINIOR_CORE_INDIGO},
     {FORM_CHANGE_BATTLE_END,        SPECIES_MINIOR_CORE_INDIGO},
     {FORM_CHANGE_END},
 };
 static const struct FormChange sMiniorOrangeFormChangeTable[] = {
+    {FORM_CHANGE_BATTLE_HP_PERCENT, SPECIES_MINIOR_METEOR_ORANGE, ABILITY_SHIELDS_DOWN, HP_HIGHER_THAN,   50},
+    {FORM_CHANGE_BATTLE_HP_PERCENT, SPECIES_MINIOR_CORE_ORANGE,   ABILITY_SHIELDS_DOWN, HP_LOWER_EQ_THAN, 50},
     {FORM_CHANGE_BATTLE_SWITCH,     SPECIES_MINIOR_CORE_ORANGE},
     {FORM_CHANGE_FAINT,             SPECIES_MINIOR_CORE_ORANGE},
     {FORM_CHANGE_BATTLE_END,        SPECIES_MINIOR_CORE_ORANGE},
     {FORM_CHANGE_END},
 };
 static const struct FormChange sMiniorVioletFormChangeTable[] = {
+    {FORM_CHANGE_BATTLE_HP_PERCENT, SPECIES_MINIOR_METEOR_VIOLET, ABILITY_SHIELDS_DOWN, HP_HIGHER_THAN,   50},
+    {FORM_CHANGE_BATTLE_HP_PERCENT, SPECIES_MINIOR_CORE_VIOLET,   ABILITY_SHIELDS_DOWN, HP_LOWER_EQ_THAN, 50},
     {FORM_CHANGE_BATTLE_SWITCH,     SPECIES_MINIOR_CORE_VIOLET},
     {FORM_CHANGE_FAINT,             SPECIES_MINIOR_CORE_VIOLET},
     {FORM_CHANGE_BATTLE_END,        SPECIES_MINIOR_CORE_VIOLET},
     {FORM_CHANGE_END},
 };
 static const struct FormChange sMiniorYellowFormChangeTable[] = {
+    {FORM_CHANGE_BATTLE_HP_PERCENT, SPECIES_MINIOR_METEOR_YELLOW, ABILITY_SHIELDS_DOWN, HP_HIGHER_THAN,   50},
+    {FORM_CHANGE_BATTLE_HP_PERCENT, SPECIES_MINIOR_CORE_YELLOW,   ABILITY_SHIELDS_DOWN, HP_LOWER_EQ_THAN, 50},
     {FORM_CHANGE_BATTLE_SWITCH,     SPECIES_MINIOR_CORE_YELLOW},
     {FORM_CHANGE_FAINT,             SPECIES_MINIOR_CORE_YELLOW},
     {FORM_CHANGE_BATTLE_END,        SPECIES_MINIOR_CORE_YELLOW},
     {FORM_CHANGE_END},
 };
-
 #endif
 
 #if P_GEN_8_POKEMON == TRUE
 static const struct FormChange sCramorantFormChangeTable[] = {
+    {FORM_CHANGE_BATTLE_HP_PERCENT, SPECIES_CRAMORANT_GULPING, ABILITY_GULP_MISSILE, HP_HIGHER_THAN,   50},
+    {FORM_CHANGE_BATTLE_HP_PERCENT, SPECIES_CRAMORANT_GORGING, ABILITY_GULP_MISSILE, HP_LOWER_EQ_THAN, 50},
     {FORM_CHANGE_BATTLE_SWITCH,     SPECIES_CRAMORANT},
     {FORM_CHANGE_FAINT,             SPECIES_CRAMORANT},
     {FORM_CHANGE_BATTLE_END,        SPECIES_CRAMORANT},

src/daycare.c

@@ -256,7 +256,8 @@ static u16 TakeSelectedPokemonFromDaycare(struct DaycareMon *daycareMon)
     BoxMonToMon(&daycareMon->mon, &pokemon);
 
     newSpecies = GetFormChangeTargetSpecies(&pokemon, FORM_CHANGE_WITHDRAW, 0);
-    if (newSpecies != SPECIES_NONE) {
+    if (newSpecies != SPECIES_NONE)
+    {
         SetMonData(&pokemon, MON_DATA_SPECIES, &newSpecies);
         CalculateMonStats(&pokemon);
         species = newSpecies;

src/pokemon.c

@@ -3999,13 +3999,14 @@ void CalculateMonStats(struct Pokemon *mon)
     {
         if (currentHP == 0 && oldMaxHP == 0)
             currentHP = newMaxHP;
-        else if (currentHP != 0) {
+        else if (currentHP != 0)
-            // BUG: currentHP is unintentionally able to become <= 0 after the instruction below. This causes the pomeg berry glitch.
+        {
+            if (newMaxHP > oldMaxHP)
                 currentHP += newMaxHP - oldMaxHP;
-            #ifdef BUGFIX
             if (currentHP <= 0)
                 currentHP = 1;
-            #endif
+            if (currentHP > newMaxHP)
+                currentHP = newMaxHP;
         }
         else
             return;
@@ -8398,12 +8399,7 @@ u16 GetFormChangeTargetSpeciesBoxMon(struct BoxPokemon *boxMon, u16 method, u32
                     if (heldItem == formChanges[i].param1 || formChanges[i].param1 == ITEM_NONE)
                         targetSpecies = formChanges[i].targetSpecies;
                     break;  
-                case FORM_CHANGE_PRIMAL_REVERSION:
-                    if (arg == formChanges[i].param1)
-                        targetSpecies = formChanges[i].targetSpecies;
-                    break;
                 case FORM_CHANGE_WITHDRAW:
-                case FORM_CHANGE_BATTLE_SWITCH:
                 case FORM_CHANGE_FAINT:
                     targetSpecies = formChanges[i].targetSpecies;
                     break;
@@ -8415,6 +8411,23 @@ u16 GetFormChangeTargetSpeciesBoxMon(struct BoxPokemon *boxMon, u16 method, u32
     return targetSpecies;
 }
 
+bool32 DoesSpeciesHaveFormChangeMethod(u16 species, u16 method)
+{
+    u32 i, j;
+    const struct FormChange *formChanges = gFormChangeTablePointers[species];
+
+    if (formChanges != NULL)
+    {
+        for (i = 0; formChanges[i].method != FORM_CHANGE_END; i++)
+        {
+            if (method == formChanges[i].method && species != formChanges[i].targetSpecies)
+                return TRUE;
+        }
+    }
+
+    return FALSE;
+}
+
 u16 MonTryLearningNewMoveEvolution(struct Pokemon *mon, bool8 firstMove)
 {
     u16 species = GetMonData(mon, MON_DATA_SPECIES, NULL);
@@ -8495,12 +8508,21 @@ bool32 ShouldShowFemaleDifferences(u16 species, u32 personality)
     return (gBaseStats[species].flags & SPECIES_FLAG_GENDER_DIFFERENCE) && GetGenderFromSpeciesAndPersonality(species, personality) == MON_FEMALE;
 }
 
+// Returns species that it transformed into. If it didn't, returns SPECIES_NONE.
 bool32 TryFormChange(u32 monId, u32 side, u16 method)
 {
-    u32 targetSpecies;
     struct Pokemon *party = (side == B_SIDE_PLAYER) ? gPlayerParty : gEnemyParty;
+    u16 targetSpecies;
+
+    if (GetMonData(&party[monId], MON_DATA_SPECIES2, 0) == SPECIES_NONE
+     || GetMonData(&party[monId], MON_DATA_SPECIES2, 0) == SPECIES_EGG)
+        return FALSE;
 
     targetSpecies = GetFormChangeTargetSpecies(&party[monId], method, 0);
+
+    if (targetSpecies == SPECIES_NONE)
+        targetSpecies = gBattleStruct->changedSpecies[monId];
+
     if (targetSpecies != SPECIES_NONE)
     {
         TryToSetBattleFormChangeMoves(&party[monId], method);
@@ -8508,6 +8530,7 @@ bool32 TryFormChange(u32 monId, u32 side, u16 method)
         CalculateMonStats(&party[monId]);
         return TRUE;
     }
+
     return FALSE;
 }