Wow, this encounter is by far, in my opinion, the hardest fight in the right wing. The hero comes with his own personal retainer, a champion level gnoblar. The trick to this encounter is that the gnoblar will enrage over time, slowly building up his damage the longer he stays alive. As well, whenever he dies, he will immediately respawn, though this will reset his damage meter back to zero, and the whole enrage process begins over again. However, each time he dies, this gives the Butcher a +50% boost to his damage. The main trick to his encounter is knowing when to bring down the gnobler, while keeping the Butcher's damage within reasonable proportions.
One tactic that's regularly used is the burst down the gnoblar when the butcher is at 66% and 33% hp. This can be pretty hit and miss, cos crits on your tanks can quickly leave them eating dirt. Be prepared to reset the boss and try again many times. Take note also that this boss likes to temporarily drop aggro to punt someone.