I was going to go out of costume, but then I suddenly realised that I had accumulated one over the previous weeks.
Let me introduce the Evil Mad Scientist.
(Yes, I know there's another EMS, but they aren't half as scary as I am.)
Talk about "be prepared" - always keep some sort of photographic device about your person, you never know when you'll need to document an Instructable!
Step 1: The Makings.
The goggles, the eyeball badge (both of which I made recently), a lab coat (mine - I'm a science teacher), a rotting corpse hand (borrowed from a colleague), and facepaints.
Step 2: The Makeup
The kit was left over from another school event, and came from a local supermarket.
First, a white base. I don't have much hair, so there was a lot of base needed covering.
Second, eye-shadows. A few dots of black around the eye-sockets, smudged in with the white, using fingertips.
Third, the blackened lips. The face-paint kit also contained black lipstick - apply to top and bottom lips, then do the mmmm thing to spread it out a bit.
Finally, the bloody head wound - we also found a tube of fake blood. After applying a smudge of red face-paint, my colleague simply drew on trails of gore. She reasoned that a true Evil Mad Scientist would not care about Health & Safety...
Step 3: The Ensemble
Despite being mainly bright white, it was surprising how easy it was to walk silently up behind a student, tap them on the shoulder (usually with the zombie hand), and then have them scream as they turned around...