After the sounds I have been hearing recently, I am still rattled. But I feel I must continue onward. Here I will collect my current thoughts as succinctly as possible.
My current belief is that Slender Men have an appreciable population. Otherwise the widespread terror they spread would not be possible. The alternatives are that they do not mate often, have a long life span, and/or reproduce asexually. Though the last is naturally absurd for a species of such physical size. These assumptions, however, are all based on the guess of humanlike travel speed, specifically on foot, which is likely incorrect.
The abilities of the species are obviously the biggest conundrum. They seem to have control over space-time to some degree. The keyword here is “seem”. It is more likely, though still rather unbelievable, that they have the ability to tap into the human mind and rearrange, put in a suspended state, and/or control thought itself. This may even extend to technology. I once called a tech savvy Slender Man ridiculous, but that may have been in error. Rudimentary skill, possibly taken from the minds of victims, could be used to stop and restart a camera, or a human may simply be commanded to do this. (For a scene in which I believe both mental and electronic control are at work, see everymanHYBRID, “Ashen Waste”, 6:00-30)
However, the biggest issue with mind control is the mechanism. Long-distance, “wireless” communication is flat out ridiculous. Emitted electromagnetic radiation could account for video equipment disruptions, or perhaps a strong electric field (a magnetic field would be obvious for hopefully equally obvious reasons, and said reasons’ absence rules it out). The human mind, however, has no method with which to accept EM radiation of any wavelength, except by proxy (the eyes, which simply do not work as “input devices” so much as passive receivers). It is more likely that a direct method is used. A fine wire covered in anesthetic could be slipped into the skin and towards the brain to affect control, unpleasant though the thought is. These, if in existence, are likely housed in the tentacles or arms. I should mention the constraint of “fine wire” was used as otherwise there would be a visible entry wound, and the appendage itself would be clearly visible. The anesthetic is to prevent the victim from noticing the attack, of course. As for potential evidence, I direct you to Marble Hornet, “Entry #22,” 6:19-21 where something is seen apparently going towards and into a person’s (Alex’s) head.This isn’t quite everything I have compiled, but I feel it covers the important ideas that I have been able to come up with for now. If anyone can find any flaws in my reasoning here or elsewhere (and I’m sure there is at least one flaw), please alert me in the comments and I will consider the implications and rework my theories.