This trophy requires you to defeat Ereshkigal in the Ultimate Lair on Floor 33. Upon killing him, you will unlock:
https://www.trueachievements.com/a181524/monster-bane-a....htmhttps://www.trueachievements.com/a181523/holy-garb-of-d....htmSo, let's get started. First, I'm going to tell you the Schemata I suggest (roughly based on the guide) and the Recovery Items I believe you should have. This solution should help you knock out Ereshkigal on Normal your first attempt in your first playthrough, at which point you'll probably want to simply reload a save to get your Recovery Items back (though you certainly don't have to if you're not worried about the Final Day's challenges).
The whole dungeon only takes about 4 hours if you take the quickest route (I'll tell you what it is), so don't worry about potentially searching for items on the last day. You do have time.
Suggested SchemataErehskigal has no weaknesses to elements, so while I say Aerora that is simply my preference and any second tier spell will work as well as any other (Aerora, Thundara, Fira and Blizzara).
For abilities, if I don't tell you a level it means it doesn't really matter. The debuffs are easy to upgrade to Lvl 3 and you should do this, but it's possible without (I had all of them at Lvl 1 and still killed him)
Additionally, not all of these items are extremely important (though some are). Use your own judgment in modifying it. I picked the easiest setup I could think of.
Splendid Admiral (purchased after Day 10 in Yusnaan Champion's Quarter - I like it for its ability to give you Bravery, but really this strategy doesn't care what you use here - it doesn't even need to be defensive)
Weapon: Sickle of the Faithful (from the random cultists approaching the boss of Main Quest 1 - if you don't have it, use whatever weapon you want and see below)
Shield: Gridanian Sigil (from one of the Canvas of Prayers quest to connect all the world's highways, available starting Day 9)
Head: Crippling Hood (earned for killing the Chocobo Eater Omega on Floor 28 of the Ultimate Lair - this is optional if you have the Sickle of the Faithful - we want Protect Thief so kill this enemy if you don't have it....if you have the weapon use whatever you want here)
Wrist: Anything (Collector Catalog if you have it and recovery items that give you buffs)
Abilities: Heavy Slash, Slow, Deprotect
L'automne (purchased in the Wildlands at Canopus Farm after Day 10 - it's the best elemental garb since it gives you 21 ATB -ra spells, but if you have those separately you can really use anything here)
Weapon: Chaos' Revenge
Shield: Noblesse Veronique (purchased in the Wildlands at the Research Camp after day 10 - the lesser versions from the same vendor are acceptable if you don't have the gil)
Head: Falcon Charm (earned from killing Aeronite - use the Silk Scarf if you do not have this)
Wrist: Dawn Gauntlets (from a Treasure Sphere in the Temple Ruins in Dead Dunes near the second viewing room)
Abilities: Aerora, Thundara, Imperil, Poison Lvl 4 (from Globot Omega on Floor 8 of the Ultimate Lair)
Equilibrium+ (Day 13 reward from Hope - the ATB recharge doesn't really matter for this strategy so any garb is fine as long as you have the abilities listed below)
Weapon: Flesh Render (earned by killing Reaver Omega on Floor 15 of the Ultimate Lair)
Shield: Noblesse Veronique
Head: Warrior Hunter's Mask (earned by killing Tiffrid Omega on Floor 18 of the Ultimate Lair - important for Brave Thief)
Wrist: Enlister's Gloves (earned by killing Skata'ne Omega on Floor 23 of the Ultimate Lair)
Abilities: Attack Lvl 4, Light Slash Lvl 3/4, Heavy Slash, Aerora
Recovery Items1. Elixir (100 Soul Seeds)
2. Ether (60 Soul Seeds, trading Unappraised Items in Ruffian, and one on Floor 32)
3. Ether
4. Refresher (Floor 30)
5. Phoenix Down (Floor 29)
6. Phoenix Down
7. Phoenix Down
8. Phoenix Down
9. Phoenix Down
10. Hero's Potion (20 Soul Seeds)
Progression Through the Ultimate LairI'm going to tell you how to progress in the quickest way possible, hitting everything really important. I won't tell you how to fight the enemies (it would simply take far too long) but none of them should be too difficult. Save before them and reload if you fail. You need to get at least 3 stars on each of them, so reload if you don't.
Make sure you ALWAYS go to the floor I tell you. There's some fairly nasty enemies in here otherwise. Try not to use EP unless you have to. Feel free to leave and heal if you want - you should have time.
All of these enemies are Last Ones. If you've already defeated them, the room will simply be empty. You can replay the fights on the Ark to improve your score on those if you see them in this list and got less than 3 stars.
Floor 1 - Hoplite
Floor 2 - Niblet
Floor 5 - Gremlin
Floor 8 - Globot (drops Poison Lvl 4)
Floor 10 (optional) - Ectopudding (drops Fira Lvl 4)
Floor 11 - Miniflan
Floor 14 - Goblin
Floor 15 - Reaver (drops Flesh Render)
Floor 18 - Tiffrid (drops Warrior Hunter's Mask)
Floor 20 - Skeleton
Floor 23 - Skata'ne (drops Enlister's Gloves)
Floor 26 - Dryad (drops Aerora Lvl 4)
Floor 28 (optional) - Chocobo Eater (drops Crippling Hood)
Floor 30 - Refresher
Floor 31 - Phoenix Down
Floor 32 - Ether
Floor 33 - Ereshkigal
How to Kill EreshkigalHere we are. We're going to zerg him. I'm fairly certain that's not intended. Expect to get zero stars and a score of 1.
He has 3 stagger levels, the last of which lasts 60 seconds before reverting. You will have to hit all 3 levels a total of 4 times. You'll die after that on this strategy.
Starting the Fight - Run around him and attack from behind for a Great start (-25% HP). Immediately begin by casting Slow and then Imperil.
Step 1 - This is the first stagger. With Imperil and Slow up, proceed to spam your favorite flavor of Aerora and build up the stagger meter. Make sure you steal any buffs the boss puts on himself with the appropriate ability (Splendid Admiral can use Protect Feeder and Equilibrium+ can use Brave/Faith Feeder). As soon as it turns red, swap to L'automne to take advantage of Chaos' Revenge for an instant stagger.
Step 2 - Immediately upon staggering him, Overclock. Start using Aerora and don't stop except to steal his buffs and keep Imperil/Slow on him. If you die or slow down for some reason, Overclock again. You can't do this all the time, but you will have a little wiggle room with EP for when things don't go perfectly. Keep doing this until the third stagger (he will be debuffed with Unprotected, which looks like a broken shield).
Step 3 - Cast Poison and Deprotect. Other debuffs don't matter for now. You have 60 seconds to hurt him. Keeping Poison up is priority. Overclock after it's up and just alternate Attack and Light Slash rapidly to do a stupid amount of damage for basically no EP cost. Overclock as much as you can here.
Step 4 - Once the third stagger ends after 60 seconds. Repeat steps 1-3 until the end. He will kill you quite a few times and that's why we have Phoenix Down. You should be able to kill him before he's able to run through all your items.
I killed him in about 5 minutes with full HP and a Phoenix Down left during the 4th time I hit the third stagger.