It's based on the "Phantom of the Opera" and the Coleto/Sarcops calvus (a native bird from the Philippines).
Dex Entry (Cothello):
It loves to mimic the voice and movement of humans. It was said to regularly hold performances in the wild for other Pokémons.
It loves attention and are highly competitive. It was said to sabotage the performances of other performers to be the center of attention.
Dex Entries (Sarcorpse)
Due to its age, Sarcorpse loses their ability to produce high-quality mimicries which led to some trainers releasing them. There were sightings of this Pokémon violently attacking Cothello from behind out of spite.
Sarcorpse develops a large blade-like apparatus in one of its wings hindering its flight. Instead, this Pokémon hones its ambush tactics.
Evolution Method:
Cothello evolves from surviving a super-effective critical attack.
by Cynical_Dio