Baku resembles a massive anthropomorphic tiger, but with four legs as well as two arms, similar to a centaur. It has unruly gray hair and pink, glowing eyes.
Baku is called the "Devourer of Dreams" by the Fire Mystic, but instead of dreams, it was shown draining the mystic power from Donatello and Raphael. It also broke off a piece of a stalagmite to use as a weapon.
The Baku (獏 or 貘) is an ancient Japanese spirit with origins in Chinese myth. Originally, it was a chimeric yōkai, normally depicted with the trunk and tusks of an elephant and a tiger's paws, among other parts. It was a good spirit, and would protect against disease and bad spirits.
Because the word also referred to the Malayan Tapir, eventually in common consciousness the tapir became conflated with the supernatural being, and the two became seen as the same entity in modern depictions. The baku's most well-known trait is that it can eat the nightmares of children who summon it, but if it is still hungry after eating a nightmare, it can feed on good dreams and positive feelings until it is sated.