I've always had this headcanon that Nightmare isn't irredeemable, but just evil enough
I admit it's like a common headcanon I give to evil characters that I like, but I really do stand by this one for Nightmare.
(In my headcanon) He has a lively happy little group that's similar to the Star Sanses, and a well kept castle that I assume he pays his taxes for. He understands his place in the multiverse and upholds the balance of it, but also takes pleasure in twisting fates and manipulating universes.
I think partly he does it for job security, because by maintaining a somewhat positive multiverse, his job becomes easier as there is less competition by other evil forces, but also more job opportunities by spreading negativity. (And people will like adapt to a negative multiverse right) Also it means by treating his group more positively, the evil sanses will be more loyal to him out of true companionship rather than a more fragile fear that could turn on him.
I feel like this is a good argument for him being somewhat more ambiguous, but I also want to say he's more evil. He does still murder, manipulate and cheat, and bring suffering to others, sometimes even going so far as to torture people.
I like the way Nightmare does evil aswell, like he can shapeshift and stuff, and he threatens and manipulates people, and toy with people's emotions and psyches. He also looks scary and intimidating, and so does all of the evil sanses with him aswell
