The nil-ar represented a distinct subspecies within the reptilian Tiss'shar species. A defining characteristic was their black scales, marked by slender red stripes encircling their eyes, wrists, ankles, and tails.
According to the Ultimate Alien Anthology, the nil-ar possess the Stealthy feat. This implies the existence of either inherent biological traits or established cultural practices that enhance their aptitude for concealment and silent movement.