2. The Slender Man - Marble Hornets (2009)
The Slender Man is a costume that would give you plenty of leeway and room for creative inspiration. Although possibly the most famous use of the character, Marble Hornets didn't create the Slenderman or his mythos; the internet did that work beforehand. Originally conceived by a Something Awful forum user named Victor Surge as an entry in a photo manipulation contest, the Slenderman is a phantasmal creation that appears as a tall, thin faceless man in a black suit, sometimes sporting tendrils or tentacles from its person, and mostly associated with stalking or stealing children. In the early pictures he was a dark mix of the bogeyman and the Pied Piper. The first real manifestation of urban legend formation on the internet, Slenderman is a real corker of a costume idea. As long as you've got the suit and the featureless face, I think you've got something. The tentacles would additionally be a nice touch, but again if you've got a few expressionless, creepy kids to stumble about with you as your agents of evil, then you've just jumped this costume into the nightmare zone. As an added caution, I should remind to limit these to trick or treating and parties. Donning this get-up and just flitting about town to unease the populace would likely result in a braining.