Yeah.

Pokemon in general have some really cool pokedex entries that make for good fan-theories, but most of them are just forgotten and never expanded on.

Mimikyu "Its actual appearance is unknown. A scholar who saw what was under its rag was overwhelmed by terror and died from the shock."

Gengar in Moon "It apparently wishes for a traveling companion. Since it was once human itself, it tries to create one by taking the lives of other humans."

This one could be a movie on it's own, about a human who met a tragic end and turned into a gengar

Houndoom "If you are burned by the flames it shoots from its mouth, the pain will never go away."

Cherubi evolves by eating the small sleeping berry attached to it