It's driving me crazy not being able to share this year's costumes as I have not yet finished them, oy. So I thought in the meantime I would share my oldest son's from last year since it's one of my favorites.
You have to check out this brilliant brain tutorial I found online here. While you're at it, you should check out the entire blog where it came from as there are lots of very creative ideas.
I didn't make mine bloody as my son isn't into that, but it makes for quite a mad scientist costume when paired with dish gloves, safety goggles, and a lab coat.
While I'm at it, I'll re-share my youngest son's costume from last year which is also a favorite. You can find my full tutorial for it over at Fiskars here.
And more costume ideas can be found here.