Entei is a massive, leonine quadruped with some mastiff qualities. It is covered in brown fur and a long, light gray cloud of smoke for a mane running along its entire back. It has gray plates on either side of the mane and a plate beneath the cream belly fur on its chest. Entei has gray paws with brown pads and black cuff-like bands on its legs. Its main faceplate is red and shaped like fins or a six-sided star. A gray plate, resembling a horseshoe mustache, covers its muzzle. It also has a yellow crest with three sloped points on its forehead and red eyes. As a whole, Entei's head appears to resemble a kabuto.
An Entei is born whenever a new volcano appears. It is also said that whenever Entei roars, a volcano erupts somewhere in the world. Entei races across grasslands at high speeds.