Nightwraith can be found in Velen.
Nightwraiths are weak against Moon Dust, Specter Oil & Yrden.
Compared to other creatures of the night — katakans, nekurats and werewolves, for example — nightwraiths (and their rarer cousins, duskwraiths) might not seem all that dangerous. After all, one might ask, how much harm could a pale, withered woman in a tattered dress do?
The answer: quite a bit. Instead of finding this out the hard way, avoid crossing fields and meadows at night at all costs