This page explains how to complete the level 90 post-Endwalker duty, The Aetherfont.
How to Unlock
The Aetherfont, a 4-player dungeon, is unlocked by the level 90 Main Scenario Quest Going Haam.
Upsweep damages all players.
Tidal Breath places an attack marker on the entire area that Lyng Bakr is facing. Move behind Lyng Bakr to avoid the attack.
Body Slam damages all players and places spikes of ice throughout the area. When Lyng Bakr casts Upsweep, the ice spikes will begin to resonate. There will be a circle attack centered on each ice pile, so keep your distance.
The next time Lyng Bakr casts Body Slam, there will be taller ice spikes. Upsweep will make them resonate, and there will be much larger circle attacks centered on each ice spike, so stay as far away from the spikes as possible.
Floodstide marks all players with circle attack markers that follow them. Players should spread apart from each other to avoid overlapping each other with their circles.
Tidalspout targets a random player with a stack marker. Unmarked players should stack together with the marked player to reduce the damage of the attack.
From now on, when the boss casts Body Slam, there will be both short and tall spikes of ice. The short spikes will go off first, so stay away from them, then after their attacks go off, move a safe distance away from the tall ice spikes.
Sonic Bloop is a high-damage attack on the player highest in the enmity list.
Battle Cry damages all players.
When the boss casts Lightning Leap, there will be a large circle attack marker. After the circle attack, there will be lines of lightning that come out of the circle where the attack occurred. Make sure not to stand on the lightning lines. While the lines are appearing, there will be another circle attack marker to avoid, which will make more lines of lightning after the circle attack.
Ripper Claw is a high-damage attack on the player highest in the enmity list.
When the boss casts Spinning Claw, there will be a large circle attack marker centered on the boss. There will be straight lines of lightning (unlike the forking lines from Lightning Leap) that come out of the circle where the attack occurred. The actual attacks are wider than these initial lightning lines, so make sure to keep your distance.
The next time the boss casts Battle Cry, the edge of the area will become unsafe.
Lightning Rampage is similar to Lightning Leap, but with more circle attacks and lightning lines.
Lightning Claw targets a random player with a stack marker. Unmarked players should stack together with the marked player to reduce the damage of the attack. After this attack, there will be a circle of lightning where the attack occurred, so be sure to move off of the lightning.
Electric Eruption damages all players and places three lightning circles in the area.
Tidal Roar damages all players.
When the boss casts Octostroke, its tentacles will appear in random locations. They will each perform a cone attack, followed by repeated line attacks from random tentacles, in the direction that the suckers are facing.
Vivid Eyes is a donut attack. The tentacles will continue performing line attacks at random.
Saline Spit places a marker over each circle area of the platform. There will soon be a circle attack marker on every circle, so stand on the spaces between the circles to avoid the attack.
Tidal Breath places an attack marker on the entire area that Octomammoth is facing. Move to the rear half of Octomammoth to avoid the attack.
Telekinesis tethers three crystals outside of the area, which is followed by laser markers that point to three of the circular areas. There will be a circle attack on these marked areas, including on the band of crystals separating the circular areas, so move to a circle that a laser isn't pointing at.
Breathstroke places an attack marker on the entire area that Octomammoth is facing. Move to the rear half of Octomammoth to avoid the attack, but also make sure not to be near any tentacles, because they will all cast Clearout, performing a cone attack in the direction that the suckers are facing.
Water Drop marks all players with circle attack markers that follow them. Players should spread apart from each other to avoid overlapping each other with their circles, and should also avoid attack markers from other attacks that the boss performs at the same time.
Completing the Quest
Defeating the boss will complete one of the quest objectives for the Main Scenario Quest The Aetherfont.