FusionDex

Klefnette appears to people who have lost their door keys and offers one of its own. This key will unlock whatever door it opens, but it can never be properly locked again, and at a later time Klefnette will slip inside to steal whatever it pleases.

An abandoned plush doll became this Pokémon. 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.