Imp

Imp is a very small, red devil-reaper mouse with black wings, little horns, and inside ears. He has a silver-white mask-shaped marking over his eyes and a bony tail. When he becomes angry, as shown in episode eight, the whites of his eyes become black, his pupils turn yellow, he starts to drool black liquid, and his teeth and horns are pointier.

in the first episode imp was inside a pocketwatch it activated when May accidently trip in the pocket watch and got struck by lightning,

Imp was banished from the Rift into a golden pocketwatch. He later meets May, and then crafts a deal with her in order to escape his banishment.