One of several mysterious Ultra Beasts. People on the street report observing those infested by it suddenly becoming violent.
One of the Ultra Beasts. It’s unclear whether or not this Pokémon is sentient, but sometimes it can be observed behaving like a young girl.
A life-form from another world, it was dubbed a UB and is thought to produce a strong neurotoxin.
It appeared in this world from an Ultra Wormhole. Nihilego appears to be a parasite that lives by feeding on people and Pokémon.
— Pokédex entries (via PokeAPI)