diff --git a/include/constants/hold_effects.h b/include/constants/hold_effects.h
index 0f364d2462..a159102932 100644
--- a/include/constants/hold_effects.h
+++ b/include/constants/hold_effects.h
@@ -155,11 +155,12 @@
 // Gen9 hold effects
 #define HOLD_EFFECT_ABILITY_SHIELD      175
 #define HOLD_EFFECT_CLEAR_AMULET        176
-#define HOLD_EFFECT_MIRROR_HERB         177 // Not implemented.
+#define HOLD_EFFECT_MIRROR_HERB         177
 #define HOLD_EFFECT_PUNCHING_GLOVE      178
 #define HOLD_EFFECT_COVERT_CLOAK        179
 #define HOLD_EFFECT_LOADED_DICE         180
-#define HOLD_EFFECT_BOOSTER_ENERGY      181 // Not implemented.
+#define HOLD_EFFECT_BOOSTER_ENERGY      181
+#define HOLD_EFFECT_OGERPON_MASK        182
 
 // Gen2 hold effect
 #define HOLD_EFFECT_BERSERK_GENE        184
diff --git a/src/battle_debug.c b/src/battle_debug.c
index b088aa73ba..c3b4ac85aa 100644
--- a/src/battle_debug.c
+++ b/src/battle_debug.c
@@ -2435,6 +2435,7 @@ static const u8 sText_HoldEffectCovertCloak[] = _("Covert Cloak");
 static const u8 sText_HoldEffectLoadedDice[] = _("Loaded Dice");
 static const u8 sText_HoldEffectBoosterEnergy[] = _("Booster Energy");
 static const u8 sText_HoldEffectBerserkGene[] = _("Berserk Gene");
+static const u8 sText_HoldEffectOgerponMask[] = _("Ogerpon Mask");
 static const u8 *const sHoldEffectNames[] =
 {
     [HOLD_EFFECT_NONE] = sText_HoldEffectNone,
@@ -2585,6 +2586,7 @@ static const u8 *const sHoldEffectNames[] =
     [HOLD_EFFECT_LOADED_DICE] = sText_HoldEffectLoadedDice,
     [HOLD_EFFECT_BOOSTER_ENERGY] = sText_HoldEffectBoosterEnergy,
     [HOLD_EFFECT_BERSERK_GENE] = sText_HoldEffectBerserkGene,
+    [HOLD_EFFECT_OGERPON_MASK] = sText_HoldEffectOgerponMask,
 };
 static const u8 *GetHoldEffectName(u16 holdEffect)
 {
diff --git a/src/battle_util.c b/src/battle_util.c
index a3711f161c..612965fff2 100644
--- a/src/battle_util.c
+++ b/src/battle_util.c
@@ -9454,6 +9454,10 @@ static inline u32 CalcMoveBasePowerAfterModifiers(u32 move, u32 battlerAtk, u32
         if (gMovesInfo[move].punchingMove)
            modifier = uq4_12_multiply(modifier, UQ_4_12(1.1));
         break;
+    case HOLD_EFFECT_OGERPON_MASK:
+        if (GET_BASE_SPECIES_ID(gBattleMons[battlerAtk].species) == SPECIES_OGERPON)
+           modifier = uq4_12_multiply(modifier, UQ_4_12(1.2));
+        break;
     }
 
     // Terastallization boosts weak, non-priority, non-multi hit moves after modifiers to 60 BP.
diff --git a/src/data/items.h b/src/data/items.h
index f97c4670c1..adfb1914a2 100644
--- a/src/data/items.h
+++ b/src/data/items.h
@@ -13659,6 +13659,8 @@ const struct Item gItemsInfo[] =
     {
         .name = HANDLE_EXPANDED_ITEM_NAME("CornrstneMask", "Cornerstone Mask"),
         .price = 0,
+        .holdEffect = HOLD_EFFECT_OGERPON_MASK,
+        .holdEffectParam = 20,
         .description = COMPOUND_STRING(
             "Allows Ogerpon to\n"
             "wield the Rock-\n"
@@ -13674,6 +13676,8 @@ const struct Item gItemsInfo[] =
     {
         .name = HANDLE_EXPANDED_ITEM_NAME("WellsprngMask", "Wellspring Mask"),
         .price = 0,
+        .holdEffect = HOLD_EFFECT_OGERPON_MASK,
+        .holdEffectParam = 20,
         .description = COMPOUND_STRING(
             "Allows Ogerpon to\n"
             "wield the Water-\n"
@@ -13689,6 +13693,8 @@ const struct Item gItemsInfo[] =
     {
         .name = HANDLE_EXPANDED_ITEM_NAME("HrthflameMask", "Hearthflame Mask"),
         .price = 0,
+        .holdEffect = HOLD_EFFECT_OGERPON_MASK,
+        .holdEffectParam = 20,
         .description = COMPOUND_STRING(
             "Allows Ogerpon to\n"
             "wield the Fire-\n"
diff --git a/test/battle/hold_effect/ogerpon_mask.c b/test/battle/hold_effect/ogerpon_mask.c
new file mode 100644
index 0000000000..31fb0511f4
--- /dev/null
+++ b/test/battle/hold_effect/ogerpon_mask.c
@@ -0,0 +1,36 @@
+#include "global.h"
+#include "test/battle.h"
+
+ASSUMPTIONS
+{
+    ASSUME(gItemsInfo[ITEM_CORNERSTONE_MASK].holdEffect == HOLD_EFFECT_OGERPON_MASK);
+    ASSUME(gItemsInfo[ITEM_WELLSPRING_MASK].holdEffect == HOLD_EFFECT_OGERPON_MASK);
+    ASSUME(gItemsInfo[ITEM_HEARTHFLAME_MASK].holdEffect == HOLD_EFFECT_OGERPON_MASK);
+    ASSUME(gItemsInfo[ITEM_CORNERSTONE_MASK].holdEffectParam == 20);
+    ASSUME(gItemsInfo[ITEM_WELLSPRING_MASK].holdEffectParam == 20);
+    ASSUME(gItemsInfo[ITEM_HEARTHFLAME_MASK].holdEffectParam == 20);
+}
+
+SINGLE_BATTLE_TEST("Ogerpon Masks increase the base power of moves by 20%", s16 damage)
+{
+    u32 species;
+    u32 item;
+    PARAMETRIZE { species = SPECIES_OGERPON_TEAL_MASK; item = ITEM_NONE; }
+    PARAMETRIZE { species = SPECIES_OGERPON_WELLSPRING_MASK; item = ITEM_CORNERSTONE_MASK; }
+    PARAMETRIZE { species = SPECIES_OGERPON_HEARTHFLAME_MASK; item = ITEM_WELLSPRING_MASK; }
+    PARAMETRIZE { species = SPECIES_OGERPON_CORNERSTONE_MASK; item = ITEM_HEARTHFLAME_MASK; }
+
+    GIVEN {
+        ASSUME(gMovesInfo[MOVE_TACKLE].power > 0);
+        PLAYER(species) { Item(item); }
+        OPPONENT(SPECIES_WOBBUFFET);
+    } WHEN {
+        TURN { MOVE(player, MOVE_TACKLE); }
+    } SCENE {
+        HP_BAR(opponent, captureDamage: &results[i].damage);
+    } FINALLY {
+        EXPECT_MUL_EQ(results[0].damage, Q_4_12(1.2), results[1].damage);
+        EXPECT_MUL_EQ(results[0].damage, Q_4_12(1.2), results[2].damage);
+        EXPECT_MUL_EQ(results[0].damage, Q_4_12(1.2), results[3].damage);
+    }
+}