Shadar-Kai

The Shadar-Kai are the Elves who, following the Death of the Elven God Correlon, went to the Shadowfell and embraced the powers there. They are nearly immune to the negative energies of the Shadowfell, its corrupting depressive influence and thrived since they left the Material Plane. The Shadar-Kai have worked to maintain their portion of the Shadowfell and they have become very isolated during their time there. When any visitor or outsider could be an agent of the Banished Gods then it makes sense that they are so wary.
The Shadar-Kai themselves have made use of the dark energies of their new home. They can wield the powers of Shadows and Darkness within the Shadowfell and as such they are extremely dangerous to approach.