Rampages often. Has about 400k HPs.
At the risk of stating the obvious (to some) the key to killing these with a small force (like one group opf 65s) is to keep both the main tank and the rampage tank alive. Then the dps can nuke away without overdoing it and beat the mob down gradually. Slowing helps a lot, obviously, and it isn't easy since he's quite resistant. Tash plus Malo helps and you might still have to rely on the shaman disease slow, which isn't as good. But any level of slow makes a huge difference, natch.
Ironically, I found my warrior and my paladin, the MT and the ramp tank, did the most damage, and my casters were well behind. But that's because it was a long fight and the casting had to be paced so as to avoid grabbing aggro.