The Obsidian Mirror is an animus-touched, oval-shaped piece of glittering black obsidian. Greatness was supposed to use it to spy on the RainWings, but did not, due to the fact that she did not trust any items created by animus dragons. It is said to not have performed as well after something may have been done to it by Stonemover. In The Brightest Night, Sunny described it as a kind of horrible, sick, slithering sensation through her blood, as if it were pulling something out of Sunny's heart. She said it has a chilling wrongness to it, like the NightWing tunnels, that made Sunny's scales feel as if invisible spiders were crawling all over her. There is a theory that the mirror was enchanted by Darkstalker, as in Moon Rising he says "Enchant this mirror to spy on whichever dragon I choose" as an example of a spell.
It can be activated by saying the name of the dragon that you want to see, then by breathing smoke onto it. The dragons appear as colored tendrils of smoke, making vision unclear, but voices and background noises can be heard perfectly clear. In order to end the connection, one must breathe fire over the surface of it, so this makes it impossible for IceWings, RainWings, SeaWings or any of the Pantalan tribes to use the mirror, as they cannot breathe smoke or fire.
Preyhunter salvaged it from the NightWing island before the eruption. The mirror was first used by Preyhunter to check if Glory and her friends had noticed that they had kidnapped Sunny. He stated that it didn't work as well as it used to, and that Stonemover may have done something to it before he disappeared. After she escaped, Sunny stole the mirror and used it to follow her captors to the desert. To keep it safe, she buried it in the sand before entering the Scorpion Den, following the NightWings. In the epilogue, Sunny tried to retrieve the mirror but she couldn't find it, not knowing whether it had been stolen or swallowed by the dunes.
Darkstalker indirectly mentioned the mirror when explaining his how his scroll worked to Moonwatcher, using the phrase "enchant this mirror to spy on whichever dragons I choose" as an example.
Cobra, Qibli, and Winter visited Vulture's compound, and then asked about the Obsidian Mirror. Winter answered, saying the NightWings used it to eavesdrop on any conversation anywhere in Pyrrhia. Then Cobra suggested they steal it from her father's treasury, and revealed Vulture found the Mirror a few months prior, which is why he knew so much about Winter and Thorn. Later, Cobra returned with a sack over her shoulder, and proceeded to enter Vulture's treasury. She ordered Qibli, Winter, and Ostrich to fly to the palace, saying she would meet them there. After some conversation with Thorn, Smolder, and Typhoon, Qibli asked Thorn to arrest Cobra. It is revealed Cobra had been spying on Queen Thorn using the Obsidian Mirror, along with Vulture. Qibli ordered four Outclaws to open Cobra's sack, revealing the Obsidian Mirror, chakrams, knives, a black hood, a small glass vial that contained emerald-green liquid, and a dragonflame cactus.
Qibli told Thorn that Vulture had the Mirror for a couple of months, horrifying Thorn. Qibli then suggested they check on Queen Glacier, since she was in danger from the plague. Thorn activated the Mirror, and three IceWings were having a conversation, discussing who would take charge while Glacier was ill. They then came to the consensus that "everyone is too sick to take charge", and wondered allowed if any IceWings were healthy enough to go to the Kingdom of Sand, shocking both Winter and Thorn.
Later, Qibli used it to check on Moon, Turtle, Darkstalker, and Tsunami, who he finds is captured by an unknown dragon (later revealed to be Foeslayer). When they headed off, Qibli left the mirror with Thorn.