“Born in magic, the ancient city of Amdapor lived in splendor and died in agony. As the Fifth Astral Era gave way to the Sixth Umbral and the ensuing catastrophe, the agent of Amdapor's destruction slept. Now, the seal that has held so long is softening like windfallen fruit─and what blind worms writhe underneath the skin of the dead city?”
The Decaying Gourmand will inflict a random player with Prey. The person targeted with prey will get sucked in and eaten by the Decaying Gourmand. When they do, attack the Voracious Maw to break out the person eaten. Decaying Gourmand will also drop AoE circles on the ground that remain there, inflicting damage over time to whoever stays in it.
At first there will be a single Ranch Wamura add with the actual boss, Arioch, flying around. Kill it and have the tank stand in front of it when it dies. Anyone that stands in front of the Ranch Wamura when it dies will get a stacking debuff vulnerability down called Scale Flakes. The boss attacks whoever has the highest stacks of Scale Flakes, so make sure the tank is the one that gets the debuff. When the Scale Flakes debuff is running out, pull another Ranch Wamura add and kill it facing the tank. If the debuff runs out Arioch will start flying overhead, regenerating massive amounts of hp.
There are 8 doors divided into pairs of 2 in the boss room. The strategy is to have each member of your team responsible for one symbol, the blue goobbue, red demon, the light green dragon-like, and the dark green moth. Each symbol will appear above 2 doors. Make a progression of who will open their doors first, this is important for later. When you open both doors you get sucked into a void and you become immune to attacks, When Diabolos casts Ruinous Omen, you need to use the doors or the party will wipe. At the beginning of the fight have one of your party members open his first door, and leave it open, when you get to about 60% of Diabolos health, he will go to the center of the arena and start to cast Ruinous Omen, once it gets about halfway through the cast bar have the party member open his matching door. If timed right you will get into the void as soon as he casts Ruinous Omen and you won't take any damage. If your damage is halfway decent you should only see Ruinous Omen twice, so two of your party members will have to do it. Remember, you need to look around and memorize the positions of the 2 matching doors you're responsible for.
Avoid the orbs when they appear, they apply heavy and deal more damage as the debuff gets stacked on the party.
Note: have your healer take the job of opening the doors instead of the tank and dps. Open the first door when you can and stand near the matching door if needed. If done right, the group wouldn't be taking enough damage for the healer to be doing much healing.
Note: When given the buff that makes you immune to attacks, aggro may change if you have a summoner or scholar with a pet out. Diabolos may switch to the pet and they do not get the immunity buff, so summoners could use Titan at that point.