Yokai is a very broad category of Japanese supernatural entity that can include demons, ghosts, monsters, and just about any other creature from folklore, from microscopic monsters than infect your spleen to dragon-sized titanic snails. Many, but not all, are malevolent, and a goodly number are extremely specific, such as Karakasa kozo, the one-eyed, umbrella-shaped yokai that likes to sneak up on people and lick them with its long tongue.
Here’s a brief guide on identifying various yokai:
There’s also a live-action film featuring 100 of them:
Other Japanese Halloween topics: