While Nightmare is officially unable to change between his corrupted and non-corrupted form freely, it’s a popular headcanon that he can. One day, I was just like… “I kinda want to come up with an actual design for his ‘non-corrupted but still corrupted’ version,” if that makes any sense.
Then this drawing happened.
If you’re wondering why his eyes are cyan, it’s because they’re supposed to be the same color as they are when he’s corrupted. I like to imagine that they actually changed colors when he first turned into his other form.