20. As The Gods Will
Plot: Japan's high-school students are put through a series of insane death games. Think Battle Royale, but multiply the insanity by 100.
Japanese horror cinema is pretty great overall, but while American horror has seen a revival in this decade, J-Horror is facing a creative drought and no particularly well-received J-Horrors have come out for a little while. Still, there is one 2010s J-Horror film you should definitely watch and that is As the Gods Will, a demented slice of insanity from director Takashi Miike.
Honestly, this is one of the maddest horror movies you'll ever watch. Featuring endless surrealism, childhood games mixed with copious amounts of gore, evil dolls, spaceships and even a giant, man-eating cat, this movie is like nothing else you've ever seen and the amount of imagination put into this thing is extraordinary.
It's not always scary in the traditional sense, but it is gripping, suspenseful, delightful and uproariously entertaining. Seek it out and watch it; you'll be thinking about it for days.