diff --git a/include/battle.h b/include/battle.h
index 1d690a7fde..12e2caa805 100644
--- a/include/battle.h
+++ b/include/battle.h
@@ -538,6 +538,7 @@ struct BattleStruct
     bool8 friskedAbility; // If identifies two mons, show the ability pop-up only once.
     u8 sameMoveTurns[MAX_BATTLERS_COUNT]; // For Metronome, number of times the same moves has been SUCCESFULLY used.
     u16 moveEffect2; // For Knock Off
+    u16 changedSpecies[PARTY_SIZE]; // For Zygarde or future forms when multiple mons can change into the same pokemon.
 };
 
 #define GET_MOVE_TYPE(move, typeArg)                        \
diff --git a/include/constants/battle_config.h b/include/constants/battle_config.h
index 2571972ba0..fd45ff2428 100644
--- a/include/constants/battle_config.h
+++ b/include/constants/battle_config.h
@@ -19,6 +19,9 @@
 #define SPECIES_MINIOR 10003
 #define SPECIES_WISHIWASHI 0
 #define SPECIES_WISHIWASHI_SCHOOL 10004
+#define SPECIES_ZYGARDE 0 // 50%
+#define SPECIES_ZYGARDE_10 10005 // 10 %
+#define SPECIES_ZYGARDE_COMPLETE 10006 // 100 %
 
 // Items with peculiar battle effects. Remove them if they're properly placed in constant/items.h
 #define ITEM_GRISEOUS_ORB 0
diff --git a/src/battle_util.c b/src/battle_util.c
index 8bc8863eef..7aa6817aeb 100644
--- a/src/battle_util.c
+++ b/src/battle_util.c
@@ -3357,6 +3357,16 @@ u8 AbilityBattleEffects(u8 caseID, u8 battler, u8 ability, u8 special, u16 moveA
                 if ((effect = ShouldChangeFormHpBased(battler)))
                     BattleScriptPushCursorAndCallback(BattleScript_AttackerFormChangeEnd3);
                 break;
+            case ABILITY_POWER_CONSTRUCT:
+                if ((gBattleMons[battler].species == SPECIES_ZYGARDE || gBattleMons[battler].species == SPECIES_ZYGARDE_10)
+                    && gBattleMons[battler].hp <= gBattleMons[battler].maxHP / 2)
+                {
+                    gBattleStruct->changedSpecies[gBattlerPartyIndexes[battler]] = gBattleMons[battler].species;
+                    gBattleMons[battler].species = SPECIES_ZYGARDE_COMPLETE;
+                    BattleScriptPushCursorAndCallback(BattleScript_AttackerFormChangeEnd3);
+                    effect++;
+                }
+                break;
             }
         }
         break;
@@ -6851,6 +6861,13 @@ void UndoMegaEvolution(u32 monId)
         SetMonData(&gPlayerParty[monId], MON_DATA_SPECIES, &gBattleStruct->mega.playerEvolvedSpecies);
         CalculateMonStats(&gPlayerParty[monId]);
     }
+    // While not exactly a mega evolution, Zygarde follows the same rules.
+    else 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]);
+    }
 }
 
 void UndoFormChange(u32 monId, u32 side)