hmm....well you saw that giant Gir this year right? The one with the felt-like head and stuff.
Get some heavyweight/thick felt from a fabric store (Thick so it wont't flop over your face like a blanket)
Cut a circle pattern in it, and sew it together. Make sure it's big enough, and cut ears, and draw it's eyes and all that. Just an idea. (I dont know how you'll be able to see anything but y'knowwww)
I love Johnny the homicidal maniac xD