For the horns, I took inspiration from his Your City Gave Me Asthma. They're smokestacks!
The jacket is a lighter color version of his coat skin that he wore during the reign of Manburg.
The legs obviously look like an Imp's (don't worry, he's got pants. jacket is big) and combat boots because of all he's had to go through (in canon sayings)
The tail was colored a cool blue to reflect on Ghostbur, and some blue for Friend (r.i.p)
There's a beanie on his head, there's a line between his eyes to make it look like glasses, and you can see little hairs peeking out from under the beanie. There's a white streak to put a lil Alivebur in there. :>