The Black Knight
The final fight of Trial of the Champion begins after the players speak again to the announcer in the center. The Black Knight will fly down from the rafters and challenge the players. Of all fights in the instance, the fight against the Black Knight is the hardest and will especially challenge healers.
The Black Knight will fight the group first in an undead form, and will also summon a single ghoul. He is a Death Knight, and as such, curing diseases placed on the tank - especially in heroic - becomes a high priority.
During this fight, players must simply fight down the Black Knight while dealing with the ghoul, who will randomly leap and attack party members, and will explode if it gets low on health, or at the end of the first phase. The ghoul can be killed before it explodes, but players are best making sure to stay away from the ghoul when it begins its exploding animation.
The Black Knight will also randomly target a party member and use Death's Respite, which will stun the player and then send them flying backward, doing a large amount of damage. To keep players from being thrown out of range of the healers (or the healers themselves being thrown out of range), fight the Black Knight closer to the walls of the Coliseum while facing your backs to the wall.
When the Black Knight is taken down the first time, he will rise again as a skeleton and immediately call an Army of the Dead. These ghouls use the same abilities as the ghoul in the first fight, and cannot be reliably tanked. The Black Knight can also call upon these ghouls to explode at any time. Depending on the group composition, players will either want to DPS down the Black Knight immediately and ignore the ghouls, or take down the ghouls quickly to prevent them from exploding and wiping the group. As before, players will want to stay far away from ghouls that are about to explode.
During this phase, the Black Knight will also drop Desecration on the ground under random players. This does a small amount of damage each tick and also slows players severely, and players should move quickly out of the affected areas.
The Black Knight will turn into a ghost this time, and players must work on burning through this phase of the fight. His Death Knight abilities will be lost, but be replaced by two powerful abilities.
The first, Death's Bite, is a stacking party-wide debuff that inflicts damage and increases magic damage taken by 5% for each stack - powerful because the Black Knight will now be doing a large amount of magic damage.
The second, Marked for Death, is a random debuff to a single player which increases the magical damage they take by 200% for 10 seconds. This, combined with Death's Bite and the Black Knight's attacks, can quickly kill any player, even in normal mode.