After completing Bitter Harvest glide to the bottom of the helix and enter the instance. After a short conversation you will be ambushed. Kill the mordrem. Along the path you will encounter further mordrems, either defeat them or alternatively circumvent the enemies by gliding past them. Trahearne will ask you to choose two allies to take into the dream. You can choose between Canach, Caithe and Braham. You will face two 'illusions'. The easier options are Canach and Braham. This step is much easier using a ranged weapon, since you can avoid the AoE fields around the boss and the projectile attacks.
Upon entering the dream you will encounter the blighted visions of the two allies you previously chose, one at a time.
If Braham is chosen you will encounter his mother, Blighted Eir Stegalkin and Blighted Garm. Eir keeps at range, firing arrows which leave fiery tracks on the floor. Avoid these lines while attacking Garm. This is difficult as Eir keeps firing at you and teleports around. A ranged weapon will aid you in kiting both Garm and Eir. Occasionally, the ranger will port to the center of the Arena and begin rapid-firing volleys of arrows into the air. The pattern is predictable and easily avoided so long as you continue to strafe in one direction. Meanwhile, try to down Garm to force Eir to resurrect him. While she is distracted, you are able to attack her in melee range. Continue this process until both Eir and Garm are defeated and you can activate the rift.
If Canach is chosen you will encounter his blighted form, Blighted Canach. He remains at range firing black orbs and fireballs randomly. These are all easily avoided as long as you strafe in any direction. The indicators on the floor will tell you which type of attack is coming, the smaller the ring the more dangerous. The smaller red rings on the floor will stun you and allow Blighted Canach to attack you further. Make sure you dodge roll these attacks. Toward the mid way point of the battle Canach will use his shield to reflect the attacks (except for the blazing ones) back at Blighted Canach. In order for this to work you must stand behind or inside of Canach's shield bubble. Keep repeating this process until Canach tells you he can no longer block the attacks, at which point he will drop his shield and allow you to take over this role. Reflect the black orbs using the shield in order to whittle down Blighted Canach's health. Once the rift is open activate it.
If Caithe is chosen you will encounter a blighted version of the Pale Tree. The Blighted Pale Tree begins the fight by summoning small spaces on the ground that fire slow-moving black missiles in a ring around them, and creates more of them as the fight progresses. As she takes certain amounts of damage, she summons twisted sylvari to sacrifice themselves and make her stronger, followed by an arena-wide area attack. After that she adds a delayed ring attack as well as a few basic melee and ranged attacks, and this pattern follows until she reaches low health. At that point she starts using two adjacent ring attacks at the same time, and constantly has sylvari coming to sacrifice themselves to heal her and make her standard attacks stronger. Occasionally she will launch an arena-wide AoE during this time. Stay mobile and kill as many of her summons as possible to make the fight easier.
Once your two illusions are killed it is time to face Mordremoth.
Phase 1: Attack Mordremoth at close range and whittle down his health. He is very easy to fight and will do little damage. He has one straightforward swiping attack that is easily avoided. Stay at close range due to his whirling wind attack which remains active for a longer duration. Occasionally Mordemoth will leap behind you, which has no effect on damage other than to change his location in the arena.
Phase 2: Mordremoth will summon Blighted Rytlock Brimstone. Focus on the blighted version and damage it until the rift is open. Once you have a Blighted enemy at 1/4 of their health you can activate the rift which will turn the Blighted illusions into your allies. Continue to attack Mordremoth until he summons Blighted Marjory Delaqua. Repeat the same process as with Rytlock. As soon as you defeat Blighted Jory get ready to use the vents to take to the sky and glide as Mordremoth will electrify the floor. Once the floor is no longer electrified you can resume attacking Mordremoth. The arena will be crumbled on one side limiting your attack space. It is important to pay attention so you know where you can glide the next time the floor is electrified.
Phase 3: Once Mordremoth is at half health he will summon Blighted Caithe followed by Blighted Trahearne (if the character who started the instance belongs to no order; alternatively you will face Blighted versions of your old order friends: Blighted Tybalt Leftpaw, Blighted Forgal or Blighted Sieran). Attack both Blighted versions until their health is at 1/4 and then activate the rift. Mordremoth will once again electrify the floor and you must use the vents to glide, although this time around you need to dodge pieces of floor Mordremoth hurls at you as well. Further progressed gliding techniques, such as Lean Techniques, aid you during the air phase. Once the arena floor is no longer electrified continue your attack on Mordremoth.
Phase 4: Once Mordremoth is at 1/4 health he will electrify the floor once more and begin hurling stones at you. You will be left with a bridge to fly back and forth on. This will be your last time gliding as the end of the battle is near.
Phase 5: Mordremoth will send minions your way while one of your allies attempts to open the rift. Clear the minions before activating the rift which will stun Mordremoth allowing you to attack. Repeat as many times as necessary to defeat Mordremoth.
If you are defeated at any point in the fight, you will be placed in a protected shielded area. If you are doing the instance solo, simply talk to the Restart Mote to return to the area, however you will have to restart from Phase 1 of the fight, and if you are in a party, you will not be able to rejoin the fight until Mordremoth is defeated.
Extreme Mode
Extreme Mode is intended for full 5-man parties, and is activated by interacting with the Extreme Mote at the beginning of the mission. Enemies have much larger health pools and do significantly more damage than in normal mode. Completing the instance in extreme mode will unlock the Migraine achievement
Blighted Eir Blighted Eir's AoE longbow attack now tracks more aggressively, and also tracks all players in the party, so you must be careful you don't run through someone else's trail. The AoE also does much more damage, and rapidly stacks burning on anyone caught inside it. It is possible to quickly reach over 100 stacks of burning so be careful not to step inside or stop for too long. Eir's breakbar is also much longer here. The best strategy is to kill Garm as fast as possible each time he is revived so that Eir doesn't have time to use her AoE again.
Blighted Canach Blighted Canach has a much longer breakbar here than in normal mode, additionally regular Canach's shield is no longer capable of stopping the projectiles, and can not be relied on for this purpose.
Blighted Pale Tree
Blighted Pale Tree requires much higher DPS than in normal mode, as during the final 25% of her health she will spawn Sylvari continuously, making it very hard to prevent her from healing, additionally the explosions they cause when they reach her are map wide and undodgeable.
