Obsidian has black scales and sharp teeth. He is sly-looking, with a forked black tongue and a calculating, superior expression.
According to Moonwatcher, Obsidian has dark thoughts. He hates being on guard duty and being told what to do by RainWings, as well as being partnered with Bromeliad. He tried to be as cruel and commanding as possible towards Winter because he wanted to see him squirm. He is squeamish about the rainforest.
While Moonwatcher was checking if there were any dragons approaching them, she read Obsidian's mind, and described him as "someone with dark thoughts." Later on, Kinkajou flagged him down, and he escorted them to the NightWing village.