A few things to watch for during this fight:
When shrouding, the platforms under the ramps that take you into the side rooms are what trigger the shroud, not the pools of water.
If you're shrouding more than one person, they will each spawn an add when they go shade-form. Be mindful of this and don't shroud at the same time and leave your group to fight two mobs without you.
When you're in shade form you will take large amounts of damage if you go near living marnek or a living player. Make sure you stay a good distance away from your group.
When you go shroud form, your abilities are accessed from the AA window (hotkey 'V' by default). Watch your shroud buff timer carefully, It takes 5-6 seconds to run to the cleansing room and another 5-6 for the buff to be removed. Also account for confusion, the north and south rooms look the same and in the heat of things it's easy enough to get mixed up. The north room platform shrouds you, the south room platform removes the shroud. Also account that when running past marnek while rooted can get you melee'd and sometimes that leads to a stun. ALSO take into account there is a random target root lasting anywhere from 18-30 seconds and
Murphy's Law. You have I think two minutes give or take a few seconds from the time you get shrouded until the time your shroud expires and you get DT'd. Meaning don't leave it to the last second unless your group likes adding time and difficulty.
Shrouds have HUGE amounts of hit points, so don't bother trying to heal them. If you have a buffer not doing anything, a haste will make them kill wraiths faster, but isn't required. When you are shrouded and Marnek is in undead form, you want to prioritize Bane-ing him over killing wraiths, the bane ability is a fairly long range and instant cast ability, you can tab to target him, click the ability and then tab target back to your wraith in a second or two.
The wraiths are percentage based (I think 90/85/75/60/45/30/25/10ish, but that could very well be off or just flat out incorrect). If you kill them and wipe the event, when it resets your quest will have given you credit for killing them, but when you drop him to the correct percent that add will respawn (we wiped the first time we tried it and had gotten to kill two wraiths. Going back into the mission our wraith kill count on the mission was at 2/8, but we still had to kill eight wraiths on that attempt, making for a total of ten killed; two past completion of the task step). Wraiths will damage live players and stun when close to them. The wraith lure ability is a high hate ability with a decent amount of range and should be used asap to pull the wraiths away from the group.
