Very last minute decision for me to go as the Joker from Batman: The Dark Knight for Halloween tonight. Thankfully very easy. All up this character would've taken me about 15-20 minutes (with touch-ups and stuff).
You need:
White face paint (not normal paint, trust me)
Red lipstick
Black eyeshadow (cake & powder are best combos)
1 x sea sponge (from make-up stores)
Eye shadow brush(es).
1 can of green hairspray ;)
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No facepaint? Try this...
Moisturise your face thoroughly with some kind of skin cream and let it absorb into the skin
Then use some acrylic (Non-toxic! No oil-based paints) paint in place of the facepaint.
It'll be a little harder to apply but it should work well to get the same kind of coverage as the face paint.
If you need to you can also put a little of the moisturiser in with some of the paint and mix it really well just to make it spread a little easier on the skin :)