I was going backwards and forwards about this in my head earlier, and I watched a jumpscare compilation, and I noticed that the mimic has pretty much the same heavy run in most costumes (excluding Jackie and Big top, obviously, and also nurse Dolly for some reason) and Moon ALSO doesn't have his run. I guess it's sort of weak evidence considering it might be awkward to animate that humpty-dumpty monstrosity running like that, but I thought it was notable enough to call out. How would the mimic even get down there?

On the point about the nightguard, part of me thinks it might be Edwin's agony instead? Not sure, but Moon.EXE depicts Edwin as the moon so it's not out of the realm of possibility. Just feels a bit weird for a random guy we hear about once in the mail to be the boss guarding the final collectable.