From left to right, starting with Epic, I wanted him to give the energy of "weird sketchy guy you meet at a convention but is actually very chill and will help you if you're lost", or the guy running a Pokemon card trading booth dealing in SIR and EX cards. There may be a certain kind of video I got into recently. I also wanted to emphasize that he is the oldest of the mortal characters at roughly 40, 47 for most of DWTP. As for why his hair is white and makes him look signficantly older? I don't know, it just fit his character. My logic is that there was a lab experiment gone wrong. For his corrupted, nothing about him changes physically other than more scars on his face, which are hidden here by his hair, beard, and hood. He's also covered in soot here.
Nightmare makes the choice to look like he's in his 70s, even though he can shapeshift. He seems like the type to heavily believe in age = wisdom. I like to think that at some point in time, or maybe currently when he was hiring the Murder Time Trio, he uses the act of a tired old man to lure people in and get them to trust him. The covered side of his face is rotten flesh and looks like a realistic version of his skeleton counterpart, though it smells like apples instead of traditional rot so he isn't suspected of anything. He keeps it hidden under his hair, which is also in a ponytail behind his collar. If you remember my Dream design, I gave him branches wrapped around his neck and torso. I didn't have space, but Nightmare's branches are dead. He's paler than Dream because he is not getting the proper amounts of UV light and Vitamin D from the sun, unlike his brother who spends (spent) half the day outside and again, he's technically dead.
Cross was giving me a lot of issues and I couldn't decide what direction to go with his entire design. I definetely wanted him to look more rugged, battle scarred, experienced, and tired, very tired in his Corrupted state. I also thought the idea of him having X-shaped pupils was neat and I regret not drawing Ink with shaped pupils. Drawing this man with skin made me realize how revealing his torn sweater is, goodness put on a jacket. His horns would function the same way in which they're Nightmare's magic, not skull damage. I also decided to use a reference for once in my life for his metal jaw since a human body would change how it functions.
Aurora is meant to look like a female version of Passive Nightmare and has sharper features from both parents. She has sausage curls since it was a popular style for girls in the 19th century and was popular among the rich, like her father. She also inherited Ink's vitligo. Both her and Crescendo did, but hers is less subtle (Crescendo still has the bottom right cheek vitligo). This would be a massive insecurity of her's because she doesn't understand what it is or why she has it. Nightmare knows why it's there. He hates it. Ribbon taught her to cover up the spots with makeup once she was old enough. Not even he remembers his skin condition because he has a new issue of his skin being porcelain.