Obake, Bakemono (お化け・化け物) literally means, "transforming thing." "O" is an honorific prefix and "bake" is a noun form for the verb "bakeru 化ける (to change, to transform)." It can also be used more generally to refer to anything that is weird or grotesque.
Yuurei 幽霊 (apparition) According to Shinto beliefs, all people have a soul called "reikon 霊魂." When a person dies, the reikon leaves the body and joins the souls of its ancestors. However, when a person dies suddenly by murder, is slain in battle, commits suicide, or when he or she hasn't been given an appropriate funeral, the reikon may become a yuurei to seek revenge. Many yuurei are female ghosts who suffered badly in life from love, jealousy, sorrow, or regret. Male yuurei are less common.
Yuurei (like this one from "Ringu") usually appear in a white kimono (katabira かたびら), which people were buried in the old days, and have no legs. They also wear a white triangular piece of paper or cloth (hitaikakushi 額かくし) on their forehead. They usually appear between 2 and 3 a.m. Youkai 妖怪 literally means, "bewitching apparition." They include monsters, goblins, and ghouls. They usually appear at dawn or dusk. Unlike yuurei, which are the souls of the dead and downright scary, youkai are comical, bizarre and mischievous in some way. Here are some youkai.
Oni 鬼, demons or ogres, are one of the most famous youkai. They are huge and have horns. The color of their body is red, blue, or black. They usually carry a big iron club (kanabou 金棒). They are best known for guarding the gate of Buddhist hell. They also often appear in folktales. (Momotaro ももたろ, Issun-boshi 一寸母子 etc.) They are dumb, cruel, and malicious. 
On Setsubun (Feb. 3rd), there is a custom to drive away evil sprits. People scatter soybeans outside of doorways, shouting "鬼は外、福は内 Oni wa soto, Fuku wa uchi! (Demon out, Good luck in!)." Here are some expressions including oni:
1. Oni ni kanabou 鬼に金棒 (Literally means, "Oni with an iron club")
To make one invincible.
2. Oni no inuma ni sentaku 鬼のいぬまに洗濯 (Literally means, "Do laundry while oni are away")
When the cat's away, the mice will play.
3. Oni no kubi o totta you 鬼の首を取ったよう (Literally means, "As in beheading oni")
To achieve a major success.
4. Oni no me nimo namida 鬼の目にも涙 (Literally means, "A tear even in an oni's eye")
Even the hardest heart will sometimes be moved to pity.
5. Kokoro o oni ni suru 心を鬼にする (Literally means, "To make one's heart an oni's")
Harden one's heart against pity.
Kappa 河童 are supernatural creatures which live both on land and in water. They are as tall as a four or five year old child. They have a beak-like snout, and fins on their hands and feet. They also have a shell on their back, and a water-filled dish on their head. As long as the dish is full of water, kappa keep their supernatural powers. Kappa are known for dragging people into the water and pulling out their livers through their anuses (OUCH!) 
Although kappa harm people sometimes, there are also many tales where they have helped people. They are very curious. They often appear in cartoons because of their lovable images. Kappa love sumo wrestling and cucumbers. That is why cucumber sushi rolls are called "kappa maki". Kappa are excellent swimmers.
Rokurokubi ろくろ首Female monsters with long, flexible necks. They look just like ordinary humans during the day, but at night, they extend their necks to frighten or spy on people. They sometimes turn their human faces into those of demons.
Yuki-Onna 雪女, A snow woman, appears in a white kimono on a stormy night. She causes travelers to become lost and freeze to death.
Hitotsume-Kozou 一つ目小僧
A one-eyed goblin, literally has a large eye in the center of its face. It looks like the shaved head of a priest. It does not play tricks, but just scares people.There are hundreds more of these spooks, and I'll present them as I see fit.
