diff --git a/include/battle.h b/include/battle.h
index 95886b7e13..5b2ed5c6de 100644
--- a/include/battle.h
+++ b/include/battle.h
@@ -645,7 +645,7 @@ struct BattleStruct
     u8 lastMoveFailed; // as bits for each battler, for the sake of Stomping Tantrum
     u8 lastMoveTarget[MAX_BATTLERS_COUNT]; // The last target on which each mon used a move, for the sake of Instruct
     u16 tracedAbility[MAX_BATTLERS_COUNT];
-    u16 hpBefore[MAX_BATTLERS_COUNT]; // Hp of battlers before using a move. For Berserk
+    u16 hpBefore[MAX_BATTLERS_COUNT]; // Hp of battlers before using a move. For Berserk and Anger Shell.
     bool8 spriteIgnore0Hp;
     struct Illusion illusion[MAX_BATTLERS_COUNT];
     s32 aiFinalScore[MAX_BATTLERS_COUNT][MAX_BATTLERS_COUNT][MAX_MON_MOVES]; // AI, target, moves to make debugging easier
diff --git a/src/battle_util.c b/src/battle_util.c
index c9ef0b08bd..f37bd901cc 100644
--- a/src/battle_util.c
+++ b/src/battle_util.c
@@ -4161,6 +4161,13 @@ static uq4_12_t GetSupremeOverlordModifier(u32 battler)
     return modifier;
 }
 
+static bool32 HadMoreThanHalfHpNowHasLess(u32 battler)
+{
+    // Had more than half of hp before, now has less
+     return (gBattleStruct->hpBefore[battler] >= gBattleMons[battler].maxHP / 2
+             && gBattleMons[battler].hp < gBattleMons[battler].maxHP / 2);
+}
+
 u32 AbilityBattleEffects(u32 caseID, u32 battler, u32 ability, u32 special, u32 moveArg)
 {
     u32 effect = 0;
@@ -5192,9 +5199,7 @@ u32 AbilityBattleEffects(u32 caseID, u32 battler, u32 ability, u32 special, u32
             if (!(gMoveResultFlags & MOVE_RESULT_NO_EFFECT)
              && TARGET_TURN_DAMAGED
              && IsBattlerAlive(battler)
-            // Had more than half of hp before, now has less
-             && gBattleStruct->hpBefore[battler] >= gBattleMons[battler].maxHP / 2
-             && gBattleMons[battler].hp < gBattleMons[battler].maxHP / 2
+             && HadMoreThanHalfHpNowHasLess(battler)
              && (gMultiHitCounter == 0 || gMultiHitCounter == 1)
              && !(TestSheerForceFlag(gBattlerAttacker, gCurrentMove))
              && CompareStat(battler, STAT_SPATK, MAX_STAT_STAGE, CMP_LESS_THAN))
@@ -5673,8 +5678,9 @@ u32 AbilityBattleEffects(u32 caseID, u32 battler, u32 ability, u32 special, u32
             if (!(gMoveResultFlags & MOVE_RESULT_NO_EFFECT)
              && !gProtectStructs[gBattlerAttacker].confusionSelfDmg
              && TARGET_TURN_DAMAGED
+             && (gMultiHitCounter == 0 || gMultiHitCounter == 1) // Activates after all hits from a multi-hit move.
              && IsBattlerAlive(gBattlerTarget)
-             && (gBattleMons[gBattlerTarget].hp <= gBattleMons[gBattlerTarget].maxHP / 2)
+             && HadMoreThanHalfHpNowHasLess(gBattlerTarget)
              && !(TestSheerForceFlag(gBattlerAttacker, gCurrentMove)))
             {
                 gBattlerAttacker = gBattlerTarget;
diff --git a/test/battle/ability/anger_shell.c b/test/battle/ability/anger_shell.c
new file mode 100644
index 0000000000..6b916e088f
--- /dev/null
+++ b/test/battle/ability/anger_shell.c
@@ -0,0 +1,95 @@
+#include "global.h"
+#include "test/battle.h"
+
+SINGLE_BATTLE_TEST("Anger Shell activates only if the target had more than 50% of its hp")
+{
+    bool32 activates = FALSE;
+    u16 maxHp = 500, hp = 0;
+
+    PARAMETRIZE { hp = 249; activates = FALSE; }
+    PARAMETRIZE { hp = 100; activates = FALSE; }
+    PARAMETRIZE { hp = 50; activates = FALSE; }
+    PARAMETRIZE { hp = 251; activates = TRUE; }
+    PARAMETRIZE { hp = 255; activates = TRUE; }
+
+    GIVEN {
+        ASSUME(gBattleMoves[MOVE_TACKLE].power != 0);
+        PLAYER(SPECIES_WOBBUFFET) { Ability(ABILITY_ANGER_SHELL); MaxHP(maxHp); HP(hp); }
+        OPPONENT(SPECIES_WOBBUFFET);
+    } WHEN {
+        TURN { MOVE(opponent, MOVE_TACKLE); }
+    } SCENE {
+        ANIMATION(ANIM_TYPE_MOVE, MOVE_TACKLE, opponent);
+        if (activates) {
+            ABILITY_POPUP(player, ABILITY_ANGER_SHELL);
+        } else {
+            NOT ABILITY_POPUP(player, ABILITY_ANGER_SHELL);
+        }
+    } THEN {
+        if (activates) {
+            EXPECT_EQ(player->statStages[STAT_DEF], DEFAULT_STAT_STAGE - 1);
+            EXPECT_EQ(player->statStages[STAT_SPDEF], DEFAULT_STAT_STAGE - 1);
+            EXPECT_EQ(player->statStages[STAT_ATK], DEFAULT_STAT_STAGE + 1);
+            EXPECT_EQ(player->statStages[STAT_SPATK], DEFAULT_STAT_STAGE + 1);
+            EXPECT_EQ(player->statStages[STAT_SPEED], DEFAULT_STAT_STAGE + 1);
+        }
+    }
+}
+
+SINGLE_BATTLE_TEST("Anger Shell lowers Def/Sp.Def by 1 and raises Atk/Sp.Atk/Spd by 1")
+{
+    u16 maxHp = 500;
+    GIVEN {
+        ASSUME(gBattleMoves[MOVE_TACKLE].power != 0);
+        PLAYER(SPECIES_WOBBUFFET) { Ability(ABILITY_ANGER_SHELL); MaxHP(maxHp); HP(maxHp / 2 + 1); }
+        OPPONENT(SPECIES_WOBBUFFET);
+    } WHEN {
+        TURN { MOVE(opponent, MOVE_TACKLE); }
+    } SCENE {
+        ANIMATION(ANIM_TYPE_MOVE, MOVE_TACKLE, opponent);
+        ABILITY_POPUP(player, ABILITY_ANGER_SHELL);
+        ANIMATION(ANIM_TYPE_GENERAL, B_ANIM_STATS_CHANGE, player);
+        MESSAGE("Wobbuffet's Defense fell!");
+        ANIMATION(ANIM_TYPE_GENERAL, B_ANIM_STATS_CHANGE, player);
+        MESSAGE("Wobbuffet's Sp. Def fell!");
+        ANIMATION(ANIM_TYPE_GENERAL, B_ANIM_STATS_CHANGE, player);
+        MESSAGE("Wobbuffet's Attack rose!");
+        ANIMATION(ANIM_TYPE_GENERAL, B_ANIM_STATS_CHANGE, player);
+        MESSAGE("Wobbuffet's Sp. Atk rose!");
+        ANIMATION(ANIM_TYPE_GENERAL, B_ANIM_STATS_CHANGE, player);
+        MESSAGE("Wobbuffet's Speed rose!");
+    } THEN {
+        EXPECT_EQ(player->statStages[STAT_DEF], DEFAULT_STAT_STAGE - 1);
+        EXPECT_EQ(player->statStages[STAT_SPDEF], DEFAULT_STAT_STAGE - 1);
+        EXPECT_EQ(player->statStages[STAT_ATK], DEFAULT_STAT_STAGE + 1);
+        EXPECT_EQ(player->statStages[STAT_SPATK], DEFAULT_STAT_STAGE + 1);
+        EXPECT_EQ(player->statStages[STAT_SPEED], DEFAULT_STAT_STAGE + 1);
+    }
+}
+
+SINGLE_BATTLE_TEST("Anger Shell activates after all hits from a multi-hit move")
+{
+    u32 j;
+    u16 maxHp = 500;
+    GIVEN {
+        ASSUME(gBattleMoves[MOVE_DOUBLE_SLAP].effect == EFFECT_MULTI_HIT);
+        PLAYER(SPECIES_WOBBUFFET) { Ability(ABILITY_ANGER_SHELL); MaxHP(maxHp); HP(maxHp / 2 + 1); }
+        OPPONENT(SPECIES_SHELLDER) { Ability(ABILITY_SKILL_LINK); } // Always hits 5 times.
+    } WHEN {
+        TURN { MOVE(opponent, MOVE_DOUBLE_SLAP); }
+    } SCENE {
+        for (j = 0; j < 4; j++)
+        {
+            ANIMATION(ANIM_TYPE_MOVE, MOVE_DOUBLE_SLAP, opponent);
+            NOT ABILITY_POPUP(player, ABILITY_ANGER_SHELL);
+        }
+        ANIMATION(ANIM_TYPE_MOVE, MOVE_DOUBLE_SLAP, opponent);
+        ABILITY_POPUP(player, ABILITY_ANGER_SHELL);
+    } THEN {
+        EXPECT_EQ(player->statStages[STAT_DEF], DEFAULT_STAT_STAGE - 1);
+        EXPECT_EQ(player->statStages[STAT_SPDEF], DEFAULT_STAT_STAGE - 1);
+        EXPECT_EQ(player->statStages[STAT_ATK], DEFAULT_STAT_STAGE + 1);
+        EXPECT_EQ(player->statStages[STAT_SPATK], DEFAULT_STAT_STAGE + 1);
+        EXPECT_EQ(player->statStages[STAT_SPEED], DEFAULT_STAT_STAGE + 1);
+    }
+}