Mushussu is a mythical hybrid from Babylonian lore, a dragon with the hind legs of an eagle, a long neck and tail, a horned head, a snakelike tongue, a crest and a feline's forelegs. Mushussu is associated with Marduk and it would influence the Hydra of Greek myth. In Abrahamic lore, Daniel would be confronted by Mushussu.
"A beast of Babylonian origin. Its name means "angry snake." It has the head and body of a snake, the front legs of a lion, and the hind legs of a scorpion. It is one of the 11 beasts that serve Tiamat and fought with the god Marduk. For some reason, it is often later depicted carrying Marduk on its back."
A NPC Mushussu can be found in the Tokyo - Bay Area at the Fukagawa Fudo, acting as a agent of the Great Mother Goddess Mami in the delivery quest Recreating the Human Race. Seeing that Flynn is no ordinary human, he tells him the story of the goddess and introduces himself, asking for the ingredients necessary for Mami to make a new kind of human. Once the ingredients are acquired Mushussu finds it a shame that more humans aren't as useful as Flynn, as that would mean Mami wouldn't need to make new ones. Mushussu asks Flynn to bring more ingredients should he get some.
Mushussu can be found in Minami Sunamachi. It can teach Nanashi the Ziodyne, Posumudi and Axel Claw skills through its Demon Whisper. Mushussu benefits from learning Electricity and healing skills. Mushussu can evolve into Tiamat upon reaching level 52.