You could do it out of fondant but that one looks like one of those puffy plastic cake decorations to me. If you look at my photos I have alot of characters that that are made of fondant. None of mine are that puffy but if you make the fondant thicker you can do it. You could also use some styrofoam to lay the fondant ontop of.
Great thank you! That makes sense that it could be a plastic decoration. I don't think I can get anything like that in time, so I might have to do fondant!
That can be done in fondant but would require a lot of work.
you could do it in rice krispie treats too, tastier than all that fondant id say.