Angel Of Darkness

Wren is used to strange, she is the only human that works in a Fae bar. But she has a constant curiosity about the strange Fae, Fallon that comes into the bar and bearly talks but changes form every time she see's them, Fallon makes another fae weak but Wren strong and energetic, Fallon can command fae with a look but can't seem to scare Wren.
Who, and more importantly what is Fallon?