Nightmarens are the enemies native to the Night Dimension. There are two kinds, the purple electric serpents and the flying moths. I couldn't find any images of them so I looked up images of their real-life counterparts.
Fighting Tactics(Electric Snakes)
Attacking the snakes with close-range attacks isn't always a good idea. The serpents electrify their bodies, but can't hold the charge all the time. Their are times when the snakes will drop charge. Their only means of attacking is simply touching you with their electrified bodies. So long-range attacks are best.
Unlike the serpents(seem indifferent to your prescence), moths attack as soon as they spot you by flapping their wings and shooting a series of rings in your direction. They often fly too high for you to target with projectiles, but since the moths are safe to touch, you can use aerial attacks.