How do you find the Marilith Mark in Final Fantasy XII?

Answer 1

TL;DR

CBF reading? Then read the short sentences with the same heading

IntroYou find it in the area of the Zertinan Caverns known as the "Invitation to Heresy." If you have just accepted this hunt because it just appeared (before or during the first visit to King Raithwall's Tomb) - then you are nowhere near ready if did not level grind a huge amount.

In fact, the snake itself is level 38, and resides in the most dangerous location of that general area (an Esper resides in the same cavern, most monsters level high 30s). If you happen to walk into it while travelling through the; Nam-Yensa, Ogir-Yensa, Westersand or the Ozmone plains while trying to fill the map (party level less than mid 30s), then walk straight back out, most enemies will just kill you (Quickenings won't help you bridge that level gap).

TL;DR

Are all your main party members level 37 or above? Then keep reading. If not, go train.

The Setup

In any case, if you are ready, go through the Westgate of Rabanastre into the Westersand. From here (Galtea Downs), go one map south into Shimmering Horizons.

Head east, into the Zertinan Caverns. If you ended up in Giza Plains (Starfall Field), then go back, it's the other east.

Fortunately, this is the map Marilith appears. Unfortunately for us, it only appears in a specific area after 5 minutes or so, and after you've killed off all the Speartongues (the toad/frog like monsters) in this map only. Kill off all the Speartongues first (kill other monsters as well, killing them off gives XP and less distractions when fighting the Marilith), don't move away from "Invitation to Heresy", or they'll just respawn.

You may have noticed a place in the area where there is sunlight pouring through a hole in the roof and cacti underneath to the east of the cavern. If not, go back towards the entrance from the Westersand, pass through the curved path, into the fork. If you took the left/east it's slightly to your right as you come out. If you took the right/west path, then make a left and it's in front of you. Wait in the sunny area for a while. Eventually, the Marilith will appear and the battle is on.

TL;DR

Go to Westersand, S then E. Kill everything in "Invitation to Heresy" then wait in cactus area for 5 mins. Don't go into other maps when killing things.

Showtime

The first thing you do is to cast Blind and then maybe Slow. Marilith is mainly a physical attacker that has an unfortunate vulnerability to blind so make use of it. It has 54,921HP and will probably take a fair amount of health from your party so set some Gambits up for reviving the fallen/healing the wounded. It absorbs fire weak against water and immune to everything else so get someone to use water spells if your physical attacks aren't cutting it. Eventually it will go down and you will get a "Serpentwyne Must" (automatically), which you return to the petitioner to collect your reward (2200 Gil, Serpent Eye and 3 Teleport Stones). The petitioner is the barkeep back at the Sandsea in Rabanastre.

TL;DR

Cast Blind and slow. Heal when needed, use water on it. Take item to Sandsea and collect lewt/loot.

Conclusion

Is this hunt really worth it? Depends, really. Consider this:

• Is 2200 Gil going to help you that much? (more gil is always good but Marilith isn't weak)
• Are you interested in making a Serpentarius? (or eventually a Tournesol)
• Is your Teleport Stone collection severely depleted? (unlikely)
• Were you interested in the other parts of Zertinan Caverns and this happens to be around? (Esper Adrammelech is in Zertinan Caverns as well)
• Are you going for hunt completion-ism?