I had a lot of trouble finding this guy - The cave is pretty big and confusing and it's easy to miss the path to his location. Basically from the Soldier Beacon, enter the cave and continue through while hugging the left wall. The path has no deviations until the left turn and so you're looking to take the first path to your left. The actual fight is a bit annoying, not difficult but just long. You attack him, he burrows and spawns 3 smaller adds. The cave room you fight him in has two ramp paths on either side, he usually goes up either side. If you're having trouble finding him after you've killed his adds, look for his red dot on your minimap.

It's worth noting, the Scuttling Death with burrow underground and summon 3 adds, once you kill the adds, he will appear on one of the ledges to the side, this will happen 4 times, until he returns to the centre where you can kill him. To find the Scuttling Death, enter the cave, and take the narrow left path when you enter the large room in the cave, follow the path downwards and you can't miss him