A guide for the Lunar Subterrane dungeon, added in Patch 6.5—Growing Light.
How to Unlock
The Lunar Subterrane, a 4-player dungeon, is unlocked by the level 90 Main Scenario Quest Down in the Dark.
Hexing Staves places glowing staves in random locations on the floor. The boss will cast Ruinous Confluence, which will make these staves do line attacks in a cross shape. Make sure not to be in the same line with the staves to avoid this attack.
When the boss casts Shadowy Sigil, symbols will appear on the floor tiles, and the boss will have a symbol floating around itself. Don't stand on the tiles that have the same symbol as the boss.
The boss will cast Hexing Staves again, then will cast Sorcerous Shroud, which will make the staves invisible. Be sure to remember which tiles will be safe, because the boss will cast Ruinous Confluence later, making the now-invisible staves do the cross-line attacks as before.
The boss will cast Void Dark II, which 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.
From now on, three staves will appear when the boss casts Hexing Staves, so keep this in mind when finding safe spots from the Ruinous Confluence cross-line attacks.
The boss will now cast Shadowy Sigil at the same time as Void Dark II. Stand on a safe floor tile while also not overlapping your circles. This is followed by Ruinous Confluence, so be sure to stand on a safe tile from the invisible staves.
Staff Smite is a high-damage attack on the player highest in the enmity list.
Abyssal Outburst damages all players.
Sandblast damages all players.
Landslip marks the floor with lines of moving arrows. Make sure not to allow these to push you into the unsafe edge.
The boss will jump to one side of the area, then will cast Antlion March, which is marked with red line markers on the floor. Look for a safe spot where the red line did not appear, and stand there.
The Antlion March attack damages some of the stone columns, so when the boss casts Landslip, make sure that you will not be knocked into the path of one of the broken columns.
Earthen Geyser targets a random player with a stack marker. Unmarked players should stack together with the marked player to reduce the damage of the attack. This creates a large circle of quicksand, so run out of the range of this circle as soon as possible.
Pound Sand is a large circle attack centered on the boss. Move away from the boss to avoid the attack.
Old Magic damages all players.
Duplicitous Battery places circle attack markers in a spiral on the floor, followed by another set of spiraling circle attack markers. Stand in a safe spot for the first set, wait for the first attacks to go off, then move to a safe spot for the second set.
Forsaken Fount creates orbs in the area. Each orb will do a large circle attack centered on itself, so move out of the circle attack markers to avoid the attack.
The next Duplicitous Battery is paired with a set of circle attack markers that follow each player. Wait for the second set of Duplicitous Battery attacks to go off before you spread apart.
The next Forsaken Fount is paired with Contrapasso, which damages all players and splits the orbs into two halves. Each half will do a circle attack centered on itself, so move to a safe spot where you are far away from all orb halves.
Subsequent Forsaken Founts create orbs in different positions, so when the orbs split apart with Contrapasso, look carefully for places that are far away from all orb halves.
Antipodal Assault targets a random player with a line stack marker. Unmarked players should stack together in the same line with the marked player to reduce the damage of the attack.
The boss will go to the edge and cast Hard Slash, a large cone attack in front of the boss. Go near the boss without being in front of him to avoid this attack.
Twilight Phase creates glowing curved spikes in lines. These spikes will perform line attacks in the direction that they are curving outward toward, so don't stand in front of where the curves of the spikes are pointing.
When the boss casts Dark Impact, he marks part of the floor with a glowing line. There will be a large circle attack centered on the point that the line is shining on. Move far away from where the glowing line is pointing to avoid this attack.
Deaths Journey is a circle attack centered on the boss, as well as cone attacks centered on the purple lines that the boss marks the floor with. Stay away from the boss and the purple lines to avoid the attack.
Completing the Quest
Defeating the boss will complete one of the quest objectives for the Main Scenario Quest Down in the Dark.