Diablos V2 ( prime ) battle / lore idea

The amdapori ritual grounds:

Kan-E-senna (the lady who leads gridania) has had word from the elementals that diabolos' defeat only served to delay his return, his essence gathers in the ritual grounds where the amdapori first summoned him long ago, head to the amdapori ritual grounds and stop diabolos once and for all!

In the beginning Kan-E-Senna's 2 siblings (the ones in the WHM quests) will summon a dream shroud allowing one person to enter the dream realm where the heart of diabolos lies (this person will be picked at random at the beginning of the dungeon and identified by a buff dream alignment). However, ritualistic effigy's in the area are causing a disturbance in the aether making it difficult to hold open the portal to the dream realm, the rest of the party must seek out and destroy these effigy's while their ally searches for the heart. Beware as diabolos will be roaming the area, his power is too much even for you, do not engage him!

The area will be winding tunnels but with side rooms, similar to the ones in stone vigil. While the party hunts for the effigy's to extend the dream alignment buff on the person in the dream realm (an indentical map but grey and empty) they must hide in the side rooms if they see diabolos and give his position to the ally in the dream realm.

The diabolos on the outside ( Eorzea) will have level 10 vulnerability down, level 10 damage up and aggro by sight, he will lose aggro but only if you break his line of sight for a certain amount of time( I.E sprinting round a corner and hiding in a side room)
While the diabolos in the dream realm(dynamis) will have 10 vulnerability up and 10 damage down making him easily soloable

Their HP will be linked, similar to Levi's head and tail

Upon his defeat you'll be awarded with the nightmare gear from the coffer at the end, however there will also be a second coffer in the dream realm, if your party member in there can get to it before their realignment buff wears off you will also get a nightmare weapon/shield, but be fast as the effigy's will despawn upon diabolos' defeat meaning no more extensions

plot/concept credit goes to <<C&C>> master & Co ldr

I don't see how it relates to lore.
Also, Amdapori didn't summon Diabolos. The practitioner of the Black magic, to destroy them, but failed to and Diabolos was trapped.