Some additional notes:
The ghouls (both the single one on phase 1 and the eight different ones on phase 2) have an attack called
Claw, which will make them change targets. You can and should taunt the ghoul on phase 1 to reacquire aggro if that happen (unless you have a survivable DPSer burn it down first), but it's pretty much hopeless to expect to be able to control all eight on phase 2. Note that the ghoul on phase 1 can also be shackled.
To pick up the ghoul in phase 1, notice where he tosses the herald after he kills him. The herald will be raised as a ghoul at the same spot he is then.
Threat carries over between all phases. If you build enough of a threat lead in phase 1, that gives you more breathing room to kite ghouls and run out of the desecration in phase 2.
The "Marked for Death" debuff is pretty brutal in phase 3. At some point it will result in the target being hit for 10K+ damage every two seconds from Death's Bite, and no healer can keep both the target and the rest of the group up at that point unless the Black Knight dies first.
Understanding the champions' abilities is also critical.
The warrior has Mortal Strike and Bladestorm. Bladestorm does a TON of damage and melee DPS must must must move out of it.
The rogue has a stacking poison, applied through both an AE on the ground and Fan of Knives. If you have a shaman, even if the shaman is enhancement or elemental, Cleansing Totem should be used to avoid poison stacks from piling up. You need to move out of at least the AE on the ground. If the poison stacks to full, it will tick for 5k damage every three seconds.
The other three are comparatively harmless, but have some abilities to look out for:
The shaman has a ton of different heals. He has Earth Shield (dispellable), a Hex of Mending (curse), meaning that all heals to the target will also heal him, and a 40k Healing Wave (should be interrupted). Neither of these can hold up against DPS, but if you kill him second or third (common if you have both the rogue and the warrior), the Healing Wave needs to be interrupted at the very least.
The mage has a polymorph ability and if the healer gets polymorphed, you may have to worry about staying alive by yourself for a moment. Her fireballs can be reflected.
The hunter is just a ranged damage dealer -- the one problem with him is that he likes to keep his distance and controlling aggro on him can be a bit tricky.
If you can, don't tank the champions on the floorboards where they start out -- it's not uncommon for, oddly enough, line of sight issues to crop up there.
Also, hard CC doesn't work on the champions, but stuns, interrupts, dispel, and disarming does.