Nightmare Not Being Able To See Well At All, Because His Eyelight Has Had So Much Magic Forced Through

Nightmare not being able to see well at all, because his eyelight has had so much magic forced through it for so long that it basically just broke from the strain.

It's not just blurry either; he sees his own magic loose inside his eyelight- so he sees everything sorta patchy, his vision focuses and unfocuses out of his control, maybe tunnel vision, random 'blind spots', all the weird things.

Bonus: he senses the magic of others around him, maybe not just people and animals but.. Plants... Because nightmare being able to see via grass is just. Yes.

To add to this, in a sterile environment he gets disoriented very easily; he might pace in circles, he'll probably keep a defensive stance, and he'll be less responsive to everything going on around him because He Does Not Know What Is Happening and it scares him

Double bonus: Nightmare having nasty hallucinations.

Partly because of his eyelight being broken and his mind just... Filling in the blanks. Like how sometimes a heap of clothes on a chair or something can look like a person standing there when the room is dark. Except it's like that all the time. He cannot get away from it, this is just how he sees the world.

Partly because his negative magic might have an effect on his mental state.

Also partly because centuries of being corrupted and having little to no positive interactions with actual people would definitely take it's toll on one's mental health and emotional state. He can probably hardly think straight to reason that the hallucinations can't hurt him. Triple Bonus: Dust finds out about the hallucinations and is very determined to help Nightmare with the issue by any means necessary.

This could include Dust using audio cues like snapping his fingers or something to better communicate with Night, or just to get his attention and let him know he's not alone when he seems disoriented or overwhelmed

Error might use string to lay out across the base, maybe just in corners of hallways and such, so Nightmare would be able to sense the magic and know where he's going.

(I think he'd have memorized his base, but it still might take him a second sometimes, and someone points this out and Error does it despite Night's protests because he really doesn't have anything better to do)

Horror might also use audio cues, and he might get more defensive of Nightmare. He would also absolutely take advantage of Nightmare's weakness to prank him. (Dust and Killer cannot resist joining in on the chaos.

Visionn't