Shadowsingers are faeries that have the ability to wield and control shadows. They can hear and feel things others can't and can merge into the shadows as well as transport through them.
The powers of a shadowsinger are as secret and mysterious as the shadows themselves. They are incredibly stealthy. They are often surrounded by shadows and are said to have the ability to feel and hear things that others can't. They can control and manipulate shadows, merging into them or using them to transport in a manner similar to winnowing.
When Feyre first meets Azriel, she notices how he is surrounded by shadows. As she is watching his interaction with Mor, a shadow curls around his ear and he faces her quickly, as if the shadow whispered her movements to him.
It is shown that Azriel is able to hide the shadows surrounding him, as he does so when visiting the Archeron Estate to appear less "other." However, it can be inferred that it requires a lot of extra thought and focus as Azriel spends a majority of his time cloaked in shadows. The only people whose presence have made his shadows brighten and even disappear is Mor and Elain.
While on a mission with Feyre to rescue Elain, who had been kidnapped by Hybern, Azriel is able to sneak in to Hybern's camp by merging into the darkness and appearing as Feyre, disguised as Ianthe's shadow.
There is a moment in the battle of Hybern where it is said that Elain steps out of the shadows to stab Hybern, leading many people to suspect that she too has this gift. However, there is no more information on the subject.
Azriel's powers are referenced.
- Azriel - Spymaster of the Night Court