The Underground Trial/Strategy
The underground incarnate trial requires a significant amount of coordination among league members. The overall structure of the trial is a series of sequential mini-objectives. As each mini-objective is completed, a mission wide teleporter, located immediately to the right when exiting the in-trial hospital, is updated so that it will teleport folks returning from battle to the most recently secured area.
One person in the league, apparently chosen at random by the game, is assigned to lead Desdamona. This person should avoid combat whenever possible since Desdamona's death results in immediate failure.
The individual objectives are as follows:
Phase One: Initial Clearing of IDF
The rooms here are arranged in two rows of three with the initial entry point in the center of one row. Move to the right or left and clear the 3 rooms with IDF spawns. This unlocks a door to the next lower room.
Phase Two: Ritual Room
This is a standard "medium sized" Praetorian underground room, rectangular in shape. Upon entering, Desdamona will move to a point approximately 1/3 of the way across the room along its center line. Target her and move with her. The goal is to protect her from 2 spawns of IDF who will surround her and attack from all directions. Make sure the league members buffer her. These spawns are typically easy to defeat. Their arrival is shown by a clock in Desdamona's health window. Once the first pair of spawns is defeated, Desdamona will move 1/3 of the way across the room and continue the second half of the ritual. The same strategy applies here. A clock will announce the arrival of two IDF spawns and the league must defeat them to unlock the next lower level. Exit the room via an unmarked elevator in one wall near the second ritual point.
Phase Three: Tunnels and IDF Guard Room
A small room followed by a curved longer room. Stay to the right, minimize agro. The IDF forces get a bit harder here. The guard room is similar in size to the ritual room. Clearing this room will unlock the hospital teleporter feature. Exit the room via an unmarked elevator.
Phase Four: Extinction WarWalker
During this fight, the WarWalker will use a variety of AOE powers. Red text messages, including Crowd Dispersal, Targets Acquired and Lethal Force Authorized will appear on the screen. The strategy here is similar to the rings/sequestering situation in the BAF trial. If you are targeted, it is important to move QUICKLY away from the fight. Failure to do so will result in everyone being held and typically significant numbers of deaths. This is a major reason for failure at this point. The league simply cannot go into melee range and "slug it out", hoping to overcome the WarWalker's health bar.
Phase Five: Trap Room
More tunnels, during which time Devouring Earth start showing up, also Infested. The Greater Devoureds are Elite Bosses, so be careful.
Glowing mushrooms also appear. Clicking on these result in a timer bar. If successfully completed, the mushroom grants a "Lichen" temporary power. These are very important for the next AV fight.
However, first there is the trap room. A keystone shaped door (must click on it to open) leads to a room with 4 crystals at each corner. Once Desdamona moves into the room the Devouring Earth spring a trap, which holds her immobilized in the center of the room. Luckily, this is pretty far from the mobs which spawn in the room's corners. Move quickly to each corner (or split and kill 2 or more crystals at once) and kill the mobs and the crystals. They're not hard. That frees Desdamona to move forward.
Phase Six: Self Repairing / Lichen Infused Warwalkers (2)
Another series of tunnels come first, these are curved and lined with organic matter. Lots of DE mobs, more IDF. Finally, you will come to a room with a pair of ramps up both sides. This leads to the lower level guard room. Clear this room (there is a counter with Lower Level Guards Remaining), then prepare yourselves for a double AV fight. Click on the "cage" door with the spiral staircase to enter the AV room.
Self Repairing Warwalker: Move the WarWalker into the Northeast. This will position him away from the three Regenerative Lichen points. Damage dealers kill those - they keep him healed.
It is critically important to keep him in this corner as tightly as possible, ideally facing away from the league. The league should have collected 20-30 lichen powers at this point. With a tank taunting him continually toward the corner (keeping him tight), have team members spam the Lichen power on him whenever possible. As with the prior fight, being targeted means MOVE AWAY from the fight as quickly as possible. Failure to do so will result in those around you being held and if this includes the tank, the league will lose agro, the WarWalker will move away from the corner and completely regenerate his health very quickly. This will essentially mean starting the fight over with the disadvantage of having far fewer lichen temporary powers. Note that the holds/terrorized state which happens if teammates fail to move away is complete unbreakable and unresistable - and it seems to last just long enough to get everyone killed.
Lichen-infused WarWalker. Immediately upon defeating the Self Repairing Warwalker, it will respawn as the Lichen-Infused WarWalker. Use the same strategy to kill him. Note that both of these AVs within 8 minutes of entering the room grants one of the badges necessary for Master of the Underground Incarnate Trial.
When done, click on the elevator to the south.
Phase Seven: Spore Halls and Bombs
Turn on PBAOE heals. Mobs are not difficult. For the bomb badge, the accepted strategy appears to be to put one league member out ahead of the league who will site for bombs. The bombs have a detonation range which is typically longer than most range attacks but shorter than snipes. Either snipe the bombs individually from a distance, or rush and clobber them before they explode. Either strategy works for most of the bombs.
The final eight bombs are in a hallway, and packed together in such a way that approaching one to kill it will result in the next bomb being triggered. There is some discussion over whether speed boost helps or hurts here. The prevalent line of thinking appears to be that the risk of overshooting and triggering a bomb unexpectedly is too great a risk, so most leagues seem to want no use of speed boost.
After these eight bombs is a room with mobs and the final two bombs. Kill quickly, then go up the ramp on the west side of the room and down the long hallway. There is a door at the end. Go through.
Phase Eight: Avatar of Hamidon Fight
It is important to stay very close to Desdamona during this fight because proximity to her grants significant protection from the AV. Clarion incarnate powers help greatly as the AV (or seedlings?) spam confusion. A good strategy seems to be to put yourself on follow to Desdamona but target the Avatar. Have the tanks point the Avatar away from the group. Position Desdamona behind the Avatar and get in close. Kill him. He's not hard.