Fairies as such appear only in A Midsummer Night's Dream,although in The Merry Wives of Windsor a lot of people dress up asfairies. Shakespeare seems to waffle between the idea that fairieswere teeny-weeny, could sit in acorns and so on, and the idea thatthey looked just like people, which was necessary sinceordinary-sized actors had to play Titania, Oberon, Puck and so on.They were of course magical, especially good at changing theappearance of things and messing with people's minds. Like changingBottom's head to look like a donkey, for example.