Blacephalon

An awful lot of Pokémon’s names are based on puns. Whether in Japanese or English (or indeed many other localizations), names are chosen to provide a knowing nod. In the case of this hellspawn, I think it’s fair to assume Blacephalon is pointing us toward the word “blasphemy.”
(Actually it’s a lot more clever than that, but I’m doing a bit here.)
Nothing has so ever oversold the term “Ultra Beast” as this horrific clown-like aberration, with its removable head it uses as a weapon
It’s homeworld is unseeable, and according to Ultra Sun, “It slithers toward people. Then, without warning, it triggers the explosion of its own head.”
Slithers
We’re going to need more crucifixes and bibles, stat.