I had made a walkthrough on my own website forums when my set party and I were doing Zilart missions. I'll just copy paste it here as a quick reference for you guys...
ZM8 was by far the hardest part of this whole sky access string. Skill + a little bit of luck is necessary. Good luck on your runs ^^
Zilart Mission 4
1. Reset Tonberry hate:
Magephaud at I-8 in Norg. Give her 3 gold beastcoins (she gives you a key). One of the walls in the middle of F-11 in Temple of Uggalepih can be opened with the key. The Tonberry Priest will reset hate for a price.
2. Obtain Paintbrush of Souls and 4 Unlit Lanterns (done for our set so I'm not going into detail here)
3. Get to the tonberry BC:
Enter Temple from Yhoatar at H-11, go to I-10, defeat Temple Guardian to open door, go in door and head to J-7, clear out room and use paintbrush to open zone to Den of Rancor, go to E-5 and clear the room, unlit lantern people touch the Altar of Rancor to get the Rancor Flame, go to I-5 and to another map, go to E-5 and clear room, light the 4 lanterns, zone into Sacrificial Chamber, fight 3 Tonberry NMs (order to kill them is debated).
Zilart Mission 5
1. Collect 7 Elemental Fragments (key item):
Behemoth's Dominion G-9
Fight 2 Legendary Weapon NMs (can pull one at a time with sneak)
Ifrit's Cauldron L-6
Enter Ifrit's Cauldron from G-6 in Yhoatar. Head to H-8, map change, head to D-12, then J-8, then E-7, then G-7, exit to Yuhtunga Jungle at C-7. Go to K-7, kill 2 Opo-opo NMs (can trade garnet to get Opo-opo necklace).
Cape Terrigan H-5
Go to F-7 to a cave, head to H-5, kill a Shadow NM (can trade a rain lily to get Flagellant's Rope).
Sanctuary of Zi'Tah I-7
Go to J-9, then I-7, fight a flesh type NM.
Fei'Yin Cloister of Ice
Go to G-9, godownstairs, head to I-5 to the Cloister of Ice.
La Theine Plateau G-11
Enter the canyon in F-6 from the east side, go to Ordelle's Caves at F-7, go to I-6, head to H-9, climb all the way up, go to H-12, drop down the hole, go to I-11, map will change, exit at G-10 to La Theine Plateu.
West Altepa H-8
Enter Quicksand Caves from West Altepa J-9, go to K-6, drop down the hole, exit to West Altepa, go to H-8.
Zilart Mission 6
1. Obtain all 8 fragments (from ZM5)
2. Go to Quicksand Caves for an Antican BCNM fight.
West Altepa, D-12 to enter a hidden cave, enter Quicksand Caves at C-11, go to E-7, fall down pit, go north to Chamber of Oracles, fight 3 anticans (pld, rng, blm), make sure everyone has echo drops.
Zilart Mission 7
1. After ZM6 fight, touch each colored slab to put your elemental fragments in (from ZM5) to get key item.
2. Head to Delkfutt's Tower.
Zilart Mission 8
1. Go to Stellar Fulcrum in Delkfutt's Tower
If you have your key go to E-8, go to H-8 and find ???, get transported to Upper Delk's, go to F-8 through the door, go to 11th floor, go to J-6, go to 12th floor, go to F-10, zone through portal to Stellar Fulcrum.
2. Beat the NM Km'lanaut
Uses dispelga, AE gravity spell, light blade ws does massive damage, resets party hate, will use en-spells and if you nuke for that same element you heal him, nuke with opposing element.
Zilart Mission 9
1. Talk to Aldo in the Neptune's Spire.
2. Talk to Gilgamesh in Norg.
3. Go to the Sanctuary of Zitah.
Zilart Mission 10
1. Go to Ro'Maeve and zone into Hall of the Gods at H-5.
2. Observe the gate at the other end of Hall of the Gods two times.
Zilart Mission 11
1. After examining the gate, go back to Norg and talk to Gilgamesh.
2. Go to Rabao and talk to Maryoh Comyuja at G-7.
Zilart Mission 12
1. Go to Quicksand Caves.
Go to West Altepa D-12-->C-11 to Quicksand Caves, go to K-8, go through weighted door, open another door at G-8, fall down the pit, look for a ??? around where you fell.
2. Touch a ??? and kill Ancient Vessel NM.
3. Inspect the ??? to get key item.
4. Return it to Maryoh, she will then give you the Cerulean Crystal key item.
Zilart Mission 13
1. Go back to the Hall of the Gods and touch the sealed gate. You can now enter Tu'lia.