Ehhhow about this
(Keep in mind good magic affects him severely and he is highly allergic to it

Day form
Tall skinny wears white t shirt and jeans and white sneakers wears black gloves and a black mask 
Has glitchy black face with eyes that are extremely dark purple and are really just eye shapes (also glitchy) and a thin literal ear to ear smile (not always a smile but that’s the best way to describe) pointy teeth nightmare powers that are decent

Night form
The same except his mask burns up and he wears a black well fitting tailcoat suit with long tailcoats and a bow tie and black formal shoes (classic nightmare attire) much more powerful nightmare powers but nervous about using them