Nicholas's original and preferred form is a handsome youth of an average build, maybe a little on the athletic side, with quite an average height of 5'9" and a typical weight of 155lbs . His chestnut brown hair is short and quite curly, clashing with his icy blue eyes that flit from piercing to reflective to warm in an instant, their dark circles displaying a hint of redness along their edges from stress. His skin is healthily tanned but not overly so, with no scarring to speak of or tattoos or brands. His tone varies depending on however he wishes to sound, but his voice is higher in pitch than most other young men and somewhat dulled when in a neutral mood. He's quite expressive when he's faking who he is, otherwise he keeps an interested expression that can be taken many ways.
That being said this is not his true form, only the one he feels most comfortable and familiar with. Nick is of a unique species able to change his appearance nearly at will, and can assume a menagerie of different identities based on need. He can appear to be any other humanoid form of a similar size, even those of other genders, adopting new features as he sees fit to do so. Changing skin tone, hair color, and even his own voice is akin to putting on another outfit to him.
His "style" will greatly depend on what's necessary at the moment, what species he is, and what persona he adopts at the moment. None of it is set quite in stone, however if Nick has a preference it's between loose-fitting clothing that allows him more freedom to alter his body type or layered clothing that lets him more freely swap faces on the move. Baggy tees, shorts under jeans, reversible jackets, hoodies, multipurpose shoes, all of these things lend themselves to the shapeshifter's preferred "look" as far as utility goes. If necessary, he'll don some "working gear" however he prefers to blending in, not standing out.