Klefki

Once during your turn (before your attack), if this Pokémon is on your Bench, you may discard all cards attached to this Pokémon and attach it to 1 of your Pokémon as a Pokémon Tool card. Prevent any damage done to the Pokémon this card is attached to by attacks from your opponent's Mega Evolution Pokémon. If this card is attached to a Pokémon, discard this card at the end of your opponent's turn.

It never lets go of a key that it likes, so people give it the keys to vaults and safes as a way to prevent crime.