The AU Dictionary

All AU's Begining with M

Mafia AU: In which the characters are in a mafia.

Magic AU: Incorporate magic in stories where there is no magic present in canon.

Marriage Law AU: It spawn from the Marriage Law Challenge in the Harry Potter fandom, in which the premise is to forced marriage between a Muggle-born to a Pure-blood (or Half-Blood) due to a new decree passed by the Ministry of Magic to help preserve the magical population.

Master/Slave AU: In which the cast are place in an universe where slavery is an accepted economic and cultural institution. Some stories treat this as a significant moral problem to be resisted and overthrown if possible; others treat slavery as an unchangeable institution.

Merpeople AU: Or also known as Undersea AU, in which a story is set in the ocean and the characters are turned into mermaids and merman. Sometimes it's focus on only one character that becomes a mermaid or merman and another character that is a human. When it's the latter the AU usually turns into a Little Mermaid type of story.

Modern AU: In which characters from a historical (or pseudo-historical) canon universe are placed into a modern setting.

Monster AU: In which the characters are changed into non-human creatures, such as Incubus/Succubus or other kinds of monsters.