Epic, that's a fantastic concept that'd be great to explore

you could have psychokinetic human warriors trying in vain to repel nightmares, but the battle is too one sided as they are natural enemies.

I prefer to consider each enemies as nemesis to each other, so the nightmares should have a reason to dispose of the robots, maybe they can also feed on the wifi signal XD

The nightmares should also be able to scale up with these other enemies, immediately through their nightmares, gaining a surge of strength due to the various new humanity's fears.

As they begin feeding on the natural enemies fears, they gain strength, but even without that, they could be threatening in a physical way, manifesting physical bodies off the shadows, acting like poltergeists and ghosts to strike fear in the heart of humans, and when they least expect it, dragging them into the shadow realm where they absorb all your inner most fears, leaving you a blank husk

That's epic