The strat i found working best with my DK and 4 Elemental shammies for phase 2, was to blow undead army and 4 fire elementals -pop heroism- and just blow up the Black Knight. Healing usually consists of 2 casts of ele group lesser healing waves and pet sacrafice (if its up) on DK and 2-3 chain heals on elemental shammies (running DK tank within chain heal range if a top up is needed) slide the shammies out of exploding goul range when Black Knight pops his clogs. Regroup for phase 3 next to Black knight's body, re-drop totems qik heal if required then blow up ghost (every 3rd cast is a group heal).