Who are the monsters who inspire, who wreak havoc (in a good way), who can stand around with a drink and a napkin full of finger foods without looking too undignified? And especially who are the monsters who can dance to Afro-Cuban rhythms or the Buzzcocks greatest hits without bumping into stuff and possibly breaking valuable heirlooms. Not that my friend has too many of those, but you know, I'm sure there's some vintage ashtrays lying around and I would hate to break one with my mutating pod-person get-up.
Fred Gwynne as Herman Munster, pop star. The right combination of absurd horror with the added touch of sweetness. I don't think I have the stature to pull this off, but hipsters, make note: your look (and attitude) has precedent.
Creature from the Black Lagoon pinball machine. Probably a little too elaborate for such a tight costume-making deadline. Plus this would definitely be difficult to dance in. Maybe for next year.
Go as a monster-makeup tutorial. Make a YouTube frame for your face, then hang a bunch of brushes and makeup for proper product placement around your half-made-up face. Hang some arrows pointing to various facial features and "Be sure to subscribe!" banners, and you have yourself a winning costume for any occasion. Here's a scarily precocious little girl doing a Scarah Screams Monster High Doll tutorial. I wish I could be this poised on camera. Or anywhere.
Remember the poor lab assistant in Sssssss? Poor bastard. If you can't get it together for this involved costume (very Harry Potter in scope), go to the party as his terrified girlfriend. Easy, just takes large glasses, lank hair and terrified expression. You'll be the hit of the party.