Head to Grand Palace of Hu'Xzoi and check the Particle Gate (H-8 of Map 3) on the right of where you zone in for a cutscene. At this point in time your mission log will update. Check it again to pass through and head into the mission.
Note: You cannot save progress on this mission. If you wipe without a way to reraise or otherwise have to quit, you have to start from the beginning. So make sure everyone has a few hours available before you start. (At 99/ilevel the escort takes 30-40 minutes solo). You do not personally have to utilize each Quasilumin escort NPC, you merely have to reach the Ix'ghrah spawn point. You can pass through doors opened by strangers and progress through the mission.
You will need to follow the path to the end where you will need to defeat Ix'ghrah and get a cutscene. On your way there, you will run into Particle Gates that will not open. Find a nearby Cermet Alcove and check the Alcove to spawn a Quasilumin NPC. It will then progress on a pre-determined route. You can stop and start the Quasilumin much like the NPCs found in the escort quests.
You have to protect the Quasilumin while it travels to its destination. Keep the Quasilumin alive and it will open Particle Gates along its way. It will eventually reach another Cermet Alcove and once there, check the NPC again and it will open the final gate.
If the Quasilumin does not make it to the alcove, it will not open the last gate you need to progress, so travel back to the original spawn point and get a new one.
You can open the Particle Gates from the other side if you need to backtrack.
The escorted Quasilumin can be aggroed like players can. It can also be killed by AoE. Stop it well before it encounters aggressive monsters and clear them, or in the case of ghrahs, wait for them to change to their orb forms. Take care to keep it out of AoE range.
Continue to travel along, spawning new Quasilumins where needed. At times you will need to travel up and down through teleporters to change levels. There are forks in the road at points, but going the wrong way quickly leads to a dead end.
Quasilumins which are not on the move are used to get the map of the Grand Palace. If you talk to all ten, talking to one again will give you a map of this area.
One door (not an escort gate) will ask you if you want to pass through when you use it. Say no, as for now it is a one-way door and it leads back to the "lobby" at the entrance of the zone, forcing you to start over. After completing PM 8-3, the door can be used from the lobby as a shortcut to take you back to this point without needing to progress there from the standard "beginning" of the path (only for the person with PM 8-3 completed).
Some ??? along the way will also offer you a choice to return to the main room if you check them. Refuse these as well.
People who have already completed When Angels Fall can join you at this point by taking the west door from the lobby.
M1 G-4 transporter.
Continue on to M2 H-8 for the NM fight.
After your long climb you will find a Cermet Portal that opens like a normal door and beyond that another Cermet Portal. Checking it spawns an NM called Ix'ghrah. Soloable around level 80+ with Trust, trivial at Item Level.
Ix'ghrah's element varies; it is based on what day it is when Ix'ghrah is spawned, similar to Disaster Idol. It has about 8250 HP. If the day changes while you are fighting Ix'ghrah, it will change elements mid-fight.
Ix'ghrah can shift between all 4 ghrah forms; it performs a shift whenever it uses a WS. Which WS and 2-hour ability it uses depends on which form it is in at the time (it will only perform one 2HR ability). The NM's attributes are also strongly affected by which form it is in, much more so than standard ghrahs (presumably because it seems to change "jobs" with each form change, as well).
The spider form is easily damaged by both physical and magical attacks, but it is also the most dangerous form to your tank. It always uses Sickle Slash as its TP move, which ignores Utsusemi and is capable of hitting for over 1500 damage to a blink tank if it criticals. It also uses Mighty Strikes, which can make the critical a sure thing. Use caution against this form; keep HP as high as possible and kite if necessary.
The bird form is hard to hit with weapons but takes lots of damage from magic. It uses Damnation Dive as its TP move and Perfect Dodge as its 2HR.
The orb form takes more damage from weapons and less from magic. It spams either the -ga III spell for its element, or Sleepga II if it is dark elemental; no other spells will be used. If Ix'ghrah is spawned on a "bad" day (such as Lightningday) it is advised to feed it TP and get it out of this form as quickly as possible to limit the damage caused by the nuking assault. It uses Hexidiscs as its TP move and Manafont as its 2HR. Unlike standard ghrahs, the NM will only cast magic while in this form; the other forms only perform melee attacks and their standard WS/2HR.
The humanoid form doesn’t take much damage AT ALL, but doesn’t do much either, and is a good time for mages to rest for a bit of MP. It uses Vorpal Blade as its TP move and Invincible as its 2HR.
Ix'ghrah is usually vulnerable to Gravity and sometimes to Paralyze, making kiting possible if someone falls (usually to Sickle Slash), but seems more resistant, possibly immune, to Bind, Sleep and Silence. It is possible that the day that it's spawned on may determine whether or not it's vulnerable to certain enfeebles.
Healer(s) should make sure to reapply Reraise, as it seems to disappear when changing levels, before the fight. As stated above, if the party wipes and is unable to recover before finishing the mission, you have to start all over from the beginning. You don't want to lose all your progress after making it this far!
After you beat the Ix'ghrah, check the Cermet Portal for a cutscene to finish the mission.