Hei Bai

History
The spirit of a giant panda bear, normally docile and friendly, until angered where it turns into a large multi armed monster. When the Fire Nation burnt down his forest, Hei Bai transformed into its monstrous form and terrorized the nearby village, abducting one villager every night for a few days. When Aang came, Hei Bai kidnapped Sokka, the next night, he was confronted by Aang who showed Hei Bai the acorns that covered the burned forest's ground. Aang told Hei Bai the forest would come back because of the acorns. Hei Bai's anger faded and he returned to his normal form and took the acorn in his mouth and left through the village's gate. From that gate sprouted bamboo, from where the villagers stumbled through, unharmed, though Sokka seriously had to use the restroom. Oddly, although Hei Bai is a panda, his statue is modeled after a brown or black bear.

In "Siege of the North" Hei Bai returns to give Aang a ride back to the swamp's gateway, he shoots a stream of light from his mouth onto Aang, sending Aang back into the physical world. Hei Bai then blasts a disrespectful Enma into the water when he rudely comments on Aang leaving.

Hei-Bai is very docile and friendly in his panda form; when he becomes angry, though, he changes into a six-legged, black and white monster that destroys everything in its path. Somewhat vengeful and very protective of his forests, Hei-Bai generally keeps to himself and doesn't bother others unless they bother him first.

Trivia
Hei Bai (黑白) translates in Chinese as 'black-white.'