diff --git a/src/data/abilities/ability.ts b/src/data/abilities/ability.ts
index 5e7e1c2992a..0aaf5b4b124 100644
--- a/src/data/abilities/ability.ts
+++ b/src/data/abilities/ability.ts
@@ -7263,11 +7263,14 @@ export function initAbilities() {
     new Ability(AbilityId.MERCILESS, 7)
       .attr(ConditionalCritAbAttr, (_user, target, _move) => target?.status?.effect === StatusEffect.TOXIC || target?.status?.effect === StatusEffect.POISON),
     new Ability(AbilityId.SHIELDS_DOWN, 7, -1)
-      .attr(PostBattleInitFormChangeAbAttr, () => 0)
+      // Change into Meteor Form on switch-in or turn end if HP >= 50%,
+      // or Core Form if HP <= 50%.
+      .attr(PostBattleInitFormChangeAbAttr, p => p.formIndex % 7)
       .attr(PostSummonFormChangeAbAttr, p => p.formIndex % 7 + (p.getHpRatio() <= 0.5 ? 7 : 0))
       .attr(PostTurnFormChangeAbAttr, p => p.formIndex % 7 + (p.getHpRatio() <= 0.5 ? 7 : 0))
-      .conditionalAttr(p => p.formIndex !== 7, StatusEffectImmunityAbAttr)
-      .conditionalAttr(p => p.formIndex !== 7, BattlerTagImmunityAbAttr, BattlerTagType.DROWSY)
+      // All variants of Meteor Form are immune to status effects & Yawn
+      .conditionalAttr(p => p.formIndex < 7, StatusEffectImmunityAbAttr)
+      .conditionalAttr(p => p.formIndex < 7, BattlerTagImmunityAbAttr, BattlerTagType.DROWSY)
       .attr(NoFusionAbilityAbAttr)
       .attr(NoTransformAbilityAbAttr)
       .uncopiable()
@@ -7333,12 +7336,11 @@ export function initAbilities() {
       .unsuppressable()
       .bypassFaint(),
     new Ability(AbilityId.POWER_CONSTRUCT, 7)
-      .conditionalAttr(pokemon => pokemon.formIndex === 2 || pokemon.formIndex === 4, PostBattleInitFormChangeAbAttr, () => 2)
-      .conditionalAttr(pokemon => pokemon.formIndex === 3 || pokemon.formIndex === 5, PostBattleInitFormChangeAbAttr, () => 3)
-      .conditionalAttr(pokemon => pokemon.formIndex === 2 || pokemon.formIndex === 4, PostSummonFormChangeAbAttr, p => p.getHpRatio() <= 0.5 || p.getFormKey() === "complete" ? 4 : 2)
-      .conditionalAttr(pokemon => pokemon.formIndex === 2 || pokemon.formIndex === 4, PostTurnFormChangeAbAttr, p => p.getHpRatio() <= 0.5 || p.getFormKey() === "complete" ? 4 : 2)
-      .conditionalAttr(pokemon => pokemon.formIndex === 3 || pokemon.formIndex === 5, PostSummonFormChangeAbAttr, p => p.getHpRatio() <= 0.5 || p.getFormKey() === "10-complete" ? 5 : 3)
-      .conditionalAttr(pokemon => pokemon.formIndex === 3 || pokemon.formIndex === 5, PostTurnFormChangeAbAttr, p => p.getHpRatio() <= 0.5 || p.getFormKey() === "10-complete" ? 5 : 3)
+      // Change to 10% complete or 50% complete on switchout/turn end if at <50% HP;
+      // revert to 10% PC or 50% PC before a new battle starts
+      .conditionalAttr(p => p.formIndex === 4 || p.formIndex === 5, PostBattleInitFormChangeAbAttr, p => p.formIndex - 2)
+      .conditionalAttr(p => p.getHpRatio() <= 0.5 && (p.formIndex === 2 || p.formIndex === 3), PostSummonFormChangeAbAttr, p => p.formIndex + 2)
+      .conditionalAttr(p => p.getHpRatio() <= 0.5 && (p.formIndex === 2 || p.formIndex === 3), PostTurnFormChangeAbAttr, p => p.formIndex + 2)
       .attr(NoFusionAbilityAbAttr)
       .uncopiable()
       .unreplaceable()