FusionDex

The large key on Klefrill's tail varies slightly in shape among individuals, and it may occasionally swap its key for another's. It tries its key on every lock it comes across, but it never unlocks anything, which can lead to it becoming distressed.

Its tail, which is packed with nutrition, is very bouncy like a rubber ball. 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.