O Partner, My Partner - Meldacio Hunter HQ
First Available: Chapter 8
Other Requirements: Have Patch 1.13 or later
Location: Meldacio Hunter HQ
Rewards: 10,000 EXP & Magitek Suit
This quest can only be accepted if you have your game patched up to or beyond patch 1.13 for the game. To begin this quest all you need to do is speak to the man pictured above in the Meldacio Hunter HQ which is north of Lestallum and on the outskirts of the Vesperpool area, where Melusine is.
You can only fight the Melusine at night - if you challenge her to a fight before sunrise and fail to defeat her before the sun comes up then she will despawn on you in the middle of the fight. This happened to me and it was quite frustrating because all of your progress is wiped. Keep this in mind before you go into the fight.
As for the fight with Melusine, if you're below level 95 I don't recommend you even try it. You'll have to use a consumable every few seconds with how much damage she does and all the status ailments that she inflicts. It's also very unlikely that you defeat her before the sun comes up.
Melusine has a total of 1 million HP and is strong to most melee attacks (weakest to Daggers) and almost all magics (with Ice being the best to use). She also likes to inflict Poison, Stone and Confusion on your party. Her green beams inflict poison, the smoke she emits will turn anyone close to stone and lastly, her most annoying attack is she will occasionally grab someone and slap them around, inflicting confusing and almost KOing them.
The best strategy to use against Melusine is chain Tech attacks (since they make you and your party invulnerable to damage) such as Prompto's Piercer or Ignis' Overwhelm. I'd recommend avoiding straight up melee combat with Melusine as much as possible since she puts out a very heavy amount of damage.
Armiger each time it is up and if you're good enough get as many Parry attacks as you can on Noctis for Cross-Chains and damage. Despite her weakness to daggers I recommend you use the Ultima Blade against her that way you can score Blindside Links as well. Or at least switch back and forth between Daggers and the Ultima Blade.