Hrapp can be found in The Quarry, lower level in the water, all the way north in a narrow ravine. He is, as the name suggest, cloaked in fog.
Apart from being inside a nighmare zone, and being a nighmare mob himself, the attacks he has is nothing special.
I’m a little confused. The Quarry is not (no longer?) a nightmare zone. Is this rare still here? I’ve been there a couple of times and not seen him yet.