And, the finale of this little series for now, as I've decided Sni-tii and Lenn aren't able to use the Chaos Emeralds. Maybe eventually though?

Firstly, it's to be noted that Nox uses the negative energy of the Emeralds for his super form.

Appearance-wise, nearly all of Nox's body turns jet black, including his horns and spikes. His eyes, however, invert their colors. Dark mist constantly surrounds him, somewhat obscuring him apart from his eyes.

The mist around him allows him to see in bright light, and in addition to heightened durability and speed, UV light no longer harms him regardless of exposure length.

Finally, his super form allows Nox to become a shadow as long as he's not in UV light. In that form, he can stand on other shadows or crawl across surfaces on his own, though the latter tires him out quickly. Being a shadow also lets him merge with other shadows and travel with them. In either case, his shadow form or a shadow he's in are darker than they'd normally be, and in the former, his glowing eyes are always subtly visible. While he's a shadow, any exposure to UV light that would normally be dangerous to him immediately forces him back into his physical form.