Hell Teacher Nube/Nightmare Fuel


 * Hell Teacher Nube usually mixes horror and Japanese folklore with lots of comedy, but several episodes are more disturbing than funny, especially for a Shonen manga aimed at teens and pre-teens, where (save for the teachers) all the protagonists are in fifth grade.
 * One chapter has a little ghost girl who serially kidnapped several students as punishment for treating her favorite book badly...
 * A ghost girl who stole (ripped off) the legs of other children because she lost her own when she was torn in half by a train. She pulls herself with her arms, trailing guts and blood.
 * A girl who lost her best friend, so she took her remains and made a mud golem out of them. The entire school is inundated with mud that cries out in pain, ending up dissolving at the pool.
 * A procession of ghostly monks and nuns, cursed to wander forever, that appear out of torii gates (or drawings of such.) A couple of nasty, nasty schemers (a guy and his girlfriend) are tricked into stepping into their path and dragged along for all eternity.
 * A dog with a man's head, who grows attached to Kyoko. In the end, it pushes her out of the way of a falling pane of glass and is decapitated.
 * A very detailed, "visible human" doll, whose left half exposes all its internal organs, comes to life and believes itself to be a real boy, and forcefully pushes itself into anyone it could think of as a "friend." It escapes the planned exorcism and moves elsewhere, with the implication that the weird kid in the baseball cap sitting next to you might be keeping a gruesome secret...
 * A human serial killer targeting children that used the legend of 'Aka Manto' (Red Mantle) to systematically and sadistically kill children as a grudge against the kids who nearly burnt him to death in his barbershop in a prank gone wrong. Terrifying in how close he gets to killing several of Nube's students, and doubly so when he's supposed to be human (though the ending suggests that his supposed death perhaps didn't take...).