Easier than I thought. You need a kalphite task, nihil, reckless aura, scrimshaw and the other goodies I'm using there. Sharpshooter aura works alright if reckless is on cooldown. Be sure to extend both.
It's best to range, because magic can't use asphyxiate, melee can't use destroy and melee is worthless on mage phase.
Mage phase is about 80-90% outdps rate, use devo when necessary, don't be afraid to prioritize dps over dodging a couple of balls.
Melee phase is about 50% outdps if you use Onslaught.
Range phase is for building adrenaline as meleers hit too well and it stuns too often for onslaught to be effective.