Harry Potter and the Mistletoe of Doom. Luna is, of course, warning everyone about the danger of Nargles.
Well that one took a while, remind me never to put that many people in one scene again. To see this work at various stages of completion, look at the pseudo-tutorials Photoshop Colouring I [link]
and Photoshop Colouring II [link]
medium: pencil sketch, photoshop colour
EDIT: everyone gets a nose job