Attention!!! Updated strategies located here.
1
Defeat Nightmare Bugard for 15 minute time extension. Located at zone to Phomiuna Aqueducts.
Nightmare Bugard:
Awful Eye - LoS STR Down (STR-?), Petrify
Bone Crunch - ST damage, Plague
Heavy Bellow - AoE Stun
Scutum - Defense Bonus
Tail Roll - LoS damage
2
Move to third floor and set camp right at top of steps. Everyone should avoid Nightmare Hornet aggro from the hall ways on second floor and take a path directly from the bottom floor passed the altar and up the steps to third floor.
Defeat Nightmare Antlion located on third floor (not down any tunnels) for 30 Minute time extension (both Antlion and Worm must be defeated in order to get subjobs back)
Nightmare Antlion:
Mandible Bite - ST damage
Pit Ambush - heavy ST damage (on aggro)
Sandblast - AoE Blind, Silence
Venom Spray - LoS Venom (-50HP/3s)
3
Move to second floor and defeat Nightmare Worm to unlock sub jobs. Worm pops from beneath the ground at a random location in the circle around the bridge. Be sure to avoid Nightmare Hornet aggro while fighting and make sure you know where you are facing when it does draw in move.
Nightmare Worm:
Draw In (all alliance members, active or KO'd and anyone outside alliance with hate)
Sound Vacuum - AoE Silence
Stone V, Stonega III
Tremors - heavy AoE damage, DEX Down (DEX-?, diminishes)
4 Going for the win
All alliance members move north passed all of the Diablos NPCs without aggroing them. They are true sight but are not difficult to get passed if everyone is patient. Do not follow each other or the last person in the line will surely aggro a moving npc.
If someone does get aggro do not panic it is ok to aggro a single one. If more than one is aggroed you will have to fight more than one diablos at the same time which has not been done by this linkshell therefore is not recommended.
Once everyone is completely passed all the npcs have one person aggro a single NPC. This will pop a either Diablos Diamond, Heart, Club, Spade, and/or Shard (Diablos pet) which can be killed to win the zone. Once Diablos is defeated examine ??? for key item. At this point all other Diablos NPCs will despawn.
Here is some limited information I have on Diablos thanks to Teorem:
Special Abilities
Cacodemonia - AoE Curse - Diamond, Club?
Camisado - ST damage (Shard's is AoE) - Spade, Club?, Shard
Daydream - ST Charm - Diamond
Dream Shroud - MAB/MDB (dispellable) - Spade, Heart?
Hypnogenesis - LoS damage - Diamond
Nether Tempest - AoE Nether Blast (~661) - Heart
Nightmare - AoE Sleep/Bio - Diamond, Spade?
Noctoshield - Phalanx (dispellable) - Spade, Club?, Heart?
Ruinous Omen - AoE HP random % down - Club, Spade?
Sweeping Somnolence - LoS damage, Gravity - Spade
Ultimate Terror - AoE stat drain (2-5 random stats), Heart?
Dispelga - Heart?
Dispel - Club?, Heart?
Regular spells (across all): Aspir, Blindga, Bio III, Drain, Sleepga II
No time extension for winning but ??? spawns elsewhere in zone for 30 minute extension. If someone solo pops diablos and dies all diablos's will despawn and the ??? will spawn for time reguardless of whether you actually defeat Diablos so long as he depops.