What exactly do you think the role of Puck played in the story?
(Note to editor: Tried to move this to MND but wouldn't move. Please move it for me if you can. Wordprof)
Puck is one of those characters in drama whose main purpose is to move the plot forward, but who doesn't change or have a dramatic "journey" of his own -- Mercutio is the most often cited character like that. Puck is Titania's messenger and errand boy, allowing the fairy world to interact with the human world, and he is sort of the foreman of the other fairies, although Oberon and Titania are the king and queen. He also explains the deceptions and magical powers at Titania's disposal. His "Puckish" nature, playing tricks and getting into mischief, has made him a favorite for young and/or small actors and actresses (cf. Tinkerbell). As he goes about the woodland business, he expresses the fairy world's view of human actions ("Lord, what fools these mortals be"), while at the same time showing that fairy actions are whimsical as well (and, some would say, acting as Shakespeare's spokesperson.)