Nyan

Nyan (ニャーン, Nyān) is a Mysterious Being and a member of the Monster Association.

Appearance
Nyan has the appearance of an anthropomorphic cat-like monster, with light colored fur and a choker with a bell attached to it.

Monster Raid Arc
Nyan broke into Smelly Lid Prison to find Puri-Puri-Prisoner, but he wasn't there. Nyan instead decided to do business with the prisoners.

Super Fight Arc
Nyan later transformed many prisoners into monsters and they all broke out of prison.