McGonagall was always cautious with human transfiguration, Sirius Black ruined her lesson. Slugs abound, rated for questions of hermaphrodism.

James had a life changing vision. Sort of sad, in a "didn't come true" sort of way.

Dementors are really good-natured creatures that have an unfortunate thirst for knowledge. See things that the species could never tell you, but wish you knew. Involves nonsensicle ramblings about fire crabs. K for sheer creepiness of the main topic.