The other day Me, Zed, and Courin got together to "practice" tanking this mission, along with two mindblasting adjacent-AoE fire eles, and Goren flagged way back for rebirth duties. It only took 4-5 hours and 20 candy canes or so to crack.
But! we have found a strategy....
Basic idea is to aggro both groups per enemy team at once and wipe them before charging the priest. The devil is in the details.
First (mesmer boss) group we have down pretty well. Tank is best off running up once the group on the outer left is on the counterclockwise retreat north. Everyone needs to equip a bow on this one to prevent them from firing chaos storms.
Second (ele boss) group requires the tank to stand where I am, with players in the green spot to my rear left. This should catch the melee guys on the wall and sometimes a snake caster or two up on the ledge, just out of range our our midline. Between the two groups this is four melee and two arcanists; melee should easily nuke first, but beware scatter unless we have two showers going off.
Third (necro boss) group has a ton of very pesky rangers. But there is a dune-wall to be hide behind where I am standing, while the tank is up in the open. Everyone but the tank should equip wands here, to discourage the rangers from running in to throw dirt. (Not that we mind being blinded, but you *will* mind the point blank shots following). Having no weapon will not cut it, you need a wand here.
Fourth (warrior boss) group has a handful of rangers, which are again neutralized via the wall I'm behind. Tank will need to run up to get both group's attention and pull them to the spot courin is standing in.
Fifth (ranger boss) was the hardest group due to the ackward positioning. The first group patrols right outside the door, while the second one is *inside*. The method we eventually succeded with involved luring the outside group over to the sixth group, running out and letting them fight, then coming back around, pulling the inner group, killing them and then the priest. Problem is it's part luck shaking all the aggro on to the enemy team; I think there has to be a simpler way to do this, but there are 4 elementalists between the two groups who must have their earthquakes interrupted. One possibility may be to aggro the inner group through the wall, then wake up the second group and plant our tank in the door. We should be able to nuke the melee + 2 arcanists this way, then pull the last 2 arcanists out, then nail the priest.
Sixth group (monk) is full of rangers again. To neutralize them, the team waits behind the walls of the now-defeated fifth group, while the tank goes out and grabs both enemy groups and pulls them back to this location. Once all of them are dead, tank runs and gets the boss's attention, and lures him wanding just outside of the base. Then the tank waits around there, keeping the boss wanding her or someone else, while the team goes and kills the priest. As long as the boss is kept outside casting range of the priest, he won't heal the priest and that makes defeat manageable. Finishing off the boss himself can be time-consuming but between dual meteor showers and some mesmer harrasment, he will eventually fall.
Courin says she will be able to make it next week, and she's practiced this course rigorously, so I'm confident we can pull this off now. She has the timing down very well and doesn't need us rushing her or telling here when and where to go.
Some thoughts about build fine-tuning;
Possibly the most damaging thing a Blood Ritual necro can do is to power another offensive caster in need (probably mesmer depending on the bar, or eles after a long battle) Alternate ritual on monk and that caster then.
Barbed trap is probably a good addition to our ranger tank, but placed not in battle but before. Generally useful a little behind the tanking position, to catch any strays who run past the tank.
Also eruption, while expensive, can provide a little emergency protection,
but it should not be used on tanked groups as it will cause scatter.
A number of spots have us firing through walls, so minimizing the line-of-sight spells involved is probably best. While we may need fireball, phoenix can probably be replaced with incendiary bonds.
Given enough candy canes, hard rezes, quick retreats, and parking the ghostly far back, a mistake needn't require a mission restart. We must've near-wiped a ton of times trying to figure out this mission, but only restarted it once. I'd really prefer if we can get a rebirth on someone else in addition to the monk then.
Edit: fixxed for Zed