Cerberus

Cerberus lives in the Demon Lord's Castle and is known to guard the castle's treasures.

In the game Doji⭐️Maji⭐️Memorium, Cerberus served as the final boss. After the incident with Grimoire, Cerberus also patrols the Mausoleum where the Grimoire is kept.

Trivia

 * Cerberus is famously know as the guard dog of Hades in Greek Mythology.
 * Leviathan refers it as "Doggy McDogFace".
 * His growls are often mistaken as Beelzebub's stomach.