Ryūjin (龍神) is the dragon king traditionally said to live under the sea of Japan in his palace made of coral. He controls the tides with tide jewels, either kanju (干珠) or manju (満珠), the former having the ability to bring the tides out and the latter bringing them in. It is said that sea turtles, fish, and jellyfish acted as his servants.

Tengu (天狗) are a branch of yōkai that are either considered secretive protectors of mountains or demons who harass travelers depending on the period in which they appear in Japanese history or Buddhist imagery. Though initially depicted as more bird-like, they eventually became associated with a long red nose and more humanized features. 

Kitsune (狐) are supernatural foxes who have gained intelligence and magical abilities with age, denoted by how many tails - up to nine - that they have. One of their most well known abilities is that of turning into a human, especially that of a beautiful woman or an elderly man. Hoshi no Tama (ほしのたま), or Star Balls, are jewels kitsune keep in their mouth or on their tails that are said to hold some of kitsune's magical powers. If you take it from him, he will haunt you forever, but if you give it back, he will protect you with his life.

Baku (獏) are benevolent spirits that devour nightmares. It's said that if you wake up with a nightmare and chant, "Baku, baku, I give you this dream!" that he will eat it so you may never have a reoccuring nightmare. One of my personal favorite beasties from Japanese mythology :)

---

Next doing a Chinese mythology series

Exxxxxtrraaa:

Buttons for a Lakota friend.  To the left, Medicine Wheel with Red-Tailed Hawk feathers and right the Lakota flag.  The red represents the bloodshed of all men, women and children past and present against the United States government, the white teepees of traditional housing. Aho!