The Unseelie are Evil.  Not just nasty, or mischievous, but evil. They bear humanity an undying enmity, and seek constantly to corrupt and destroy humankind. They are prevented from doing so because of the terms of an ancient Compact to which they agreed upon entering this world (tricked into it, some say, by the Sidhe). By the terms of this compact, they agreed not to use their powers to destroy humanity. The Unseelie abide by the letter of this Compact, but not by its spirit. They use their supernatural power to encourage humanity's baser instincts, and delight in tricking humans into destroying themselves.  The oath is meaningless to anyone who does not believe in one God

 Still, individual humans should beware. The Compact defends Humanity, but should an individual human attract the malevolent attention of powerful Unseelie enemies, his fate could be most dire. Humans have been known to drop dead from exhaustion after a night's pursuit by the terrors of the Wild Hunt, or to plunge themselves and their entire families into ruin pursuing some will o' the wisp (literal or figurative) conjured by venomous Unseelie.

Shape Shifting (Berahku)

Inhumanly beautiful