"Some fuckwit thought they could mess with powers beyond their understanding and resurrected this ancient demon, who was otherwise just another exhibit in a museum. Had to put it down before it enslaved the entire city with the endless supply of masks it kept in that coffin. Despite my efforts, the museum staff gave me crap for destroying a 'priceless artifact'. Maybe I should've let this demon take this shithole town instead."
~Jack

A Cofagrigus styled after Mot from Shin Megami Tensei/Persona, but I substituted its horn for a long tongue.

This Pokédemon remains hidden within its sarcophagus, even attacking enemies with it. The only time it opens the coffin is to stick out its arm to cast spells, or summon masks that latch onto a victim's face to control them. Only the utter destruction of the sarcophagus will kill it and release its hold on its victims.