What is supersymmetry?
It's quite simply, really: it's a theory that when the universe was created, all particles had a counterpart, called a superparticle. Each superparticle has a slightly different "spin" than a normal particle, so they may or may not be complete copies which depends on the "unbroken supersymmetry" of the particle. This fixes some inconsistencies from the Standard Model of physics.
What does this mean and why am I telling you this?
The "spin" of a subatomic particle isn't actually spin at all. Electrons and neutrons would have to move faster than the speed of light to actually spin, which is impossible. And yet they have charges - generally negative - and thus "spin."
A supersymmetrical particle would spin differently by 1/2. Could you imagine what someone made of superparticles would look like? It would probably look somewhat similar, maybe almost like a person, but always off, always impossibly off.
Remind you of anything?
I will not state for a fact that the Slender Man is made of superparticles, for the simple reason that superparticles are still theoretical. They may or may not exist at all. It is only now that we are even discovering something that might be the Higg's boson - the particle that gives all other particles mass.
This is just something to think about.