Definitely the hardest of the three. I don't recommend entering this without animas, although I'm sure some nut has and will, and won and will win. But to me it's not worth the time to try w/o them. This thing is nasty.
Ya, this thing isn't any fun. Took out a RNG at 3/4 health with its attack called "Carousel" and almost killed me when I had full health. Tried this guy twice, lost both times.
You fight a restricted 6 person fight against a mob called Delver in this zone after you get through Promyvion-Mea. I'm sure the other crags have the same type boss fight.