At 64% he will stun, mana drain, and debuff anyone on the hate list. At 19%, will just stun and mana drain.
There is a ghost that wanders around randomly and AOE stuns/silences. The stun lasts for about 4 seconds and the silence lasts for 45 seconds, so it's imperative that casters run around the area and avoid the ghost.
Position your healers under the bridge and they should be able to reach the tank from there. Have at least three healers -- the first one will heal until 64%, then the second one will pick up as soon as everyone gets mana drained and debuffed, then the third will pick up when everyone is again mana drained at 19%.
