King's Shield protects the user from any moves except status moves for that turn. Additionally, if King's Shield blocks an attack that would make contact with the user, the attacker's Attack stat drops by 2 stages. If Sucker Punch is used on a Pokémon that has used King's Shield, the move fails and the Pokémon's Attack does not drop.
If selected by an Aegislash with Stance Change while in Blade Forme, it will change to Shield Forme immediately before it would use King's Shield, even if the move fails or is not executed due to an effect such as a status condition or confusion. Stance Change does not change the user's Forme if King's Shield is called by another move, such as Sleep Talk.
It blocks attack moves and lowers enemies' Attack. Chance of failing rises if used in a row.* You'll get the King's Shield, which protects you from physical and special moves. It also lowers the enemies' Attack. But its chance of failure rises if you use it after you use a move that evades enemies' attacks.*
In the anime
The user takes a defensive stance while it protects itself from damage. If an attacker makes direct contact with the user, the attacker's Attack is lowered.
Aegislash swirls around while in Blade Form and then turns into Shield Form. Light blue hexagonal shapes then appear one by one in front of Aegislash until they form a shield, blocking itself from attacks. If the opponent makes direct contact with the shield, they glow blue, lowering their Attack.