(spoiler?? idk honestly)

Alright, for whatever reason I absolutely cannot defeat Dia.
I think I've gotten her down to 1/2 health but she just keeps killing my party.

Party: 1 2 3

I'd like to think that my pets are pretty well armored and their prof points are in the correct places.

I think she's beaten me about 6 times, so any help would be much appreciated ^^'

Edit: I attempted her again and lost once more. Here's a video of me battling her and failing. Not sure if it'll help but it definitely can't hurt

Right, personally. I'd suggest a team that's:
Slot 1: Water or Light (I usually use my main team's Light Healer, no changes to her profs or equips and that works fine)
Slot 2: Fire
Slot 3: Air
(these exact elements in these exact slots is very much intentional)
(also + ent flasks if you feel you want or need them)

When fighting Dia there are two main times when strategy comes to more than "deal damage"- the turn of Disciple Summoning and Max Mana turn.

When you see the Icon that indicates Dia is about to summon the Disciples, you want to use Conflagrate with the fire pet.

If you're using a water tank, you can use either ice barrier or ice sphere to specifically shield the Air pet, if you have a light tank/healer just have the light pet use fairy light to hit multiple opponents and have the air pet use Block instead.

Reasoning: Conflagrate will hit Dia and both Disciples when they appear, meaning you get the most out of it. You can follow this up with Explosive Fireball. The damage from these moves allows for the Disciples to be quickly eliminated.
I notice in the video you seemed to use Thorncoat when Dia was summoning, but this wouldn't do much- the main issue when Dia summons is that she specifically Traps the pet in slot 3, disabling it for a few turns.

Hence reasoning: when Dia is summoning, either shield Air pet in slot 3 with water tank's abilities or have air pet use Block to protect itself if you choose to use Tidal Surge or Fairy Light (depending on tank element) (also why fire is specifically in slot 2, so you don't have to worry about it being Trapped or needing to block on the turn you want to get conflagrate out)

You want to get the Disciples out of the fight ASAP because they have an ability called Wrath of Du'Vahl that, as you can see at 0:38 of your video, is absolutely devastating. You can see the countdown timer to when it goes off in the Buffs section of the Disiples' info, and you really want to KO them both before it hits 0 and goes off.


And Max Mana, you just need to either Block with all pets or use Ice Sphere to shield all pets.


(and Air pet Decimate v. handy for taking out large chunks of HP on enemies with under 50% hp which is nice for speeding up the battle once you get that far)

Thank you so much! I'm training a new team with the elements needed. Hopefully I'll be able to take her down eventually