I can’t greet people with an intro, sadly, due to the character limit. The boss’d be an Ascian Lord.
Phase 1; Boss has about 30k HP. Only an incredibly weak autoattack. Once slain, two chests would pop up like the boss was fully slain. The U.I. for completing the dungeon (Commend Menu, etc.) wouldn’t, though. Anyone who walks near those chests would die instantly. HP refreshes if slain.
Phase 2; Boss has about 50k HP. A slightly strong autoattack with Fire and Blizzard to top it off, and one additional ability, named Dark, that inflicts unaspected damage and a Healing Power Down + DoT effect. FFXIV Dark is usually aimed at the healer. He’d also be able to summon 15 adds, 10 of which are incredibly tough but have nearly no damage, 5 of which have a moderate amount of HP and deal lots of damage. HP refreshes if slain.
More below. Character Limit.
Phase 3; Boss’d have about 1,500,000 HP. An incredibly strong autoattack with Fire, Blizzard, Dark, and his add-summoning to top it off, plus two more abilities, named Iota and Theta.
Iota: would deal massive damage to one single target, usually the one with the most Enmity at the time. Five second charge, one-hundred second cooldown.
Theta: main gimmick of the boss. Would deal 9,999 damage to all party members after a ‘flash’ which forces the camera to go all white. The damage is dealt when the camera fully recovers from the ‘flash’ effect. Damage is increased based on the number of Shadow Fiends alive, which it kills them all when it is executed. It deals about 2,000 more per single high-damage, mediocre-health Fiend, and about 200 more per ‘tanky’ Fiend, minus the party’s defense totaled for each person.
It’s executed one minute after summoning the Fiend adds, and also on the boss’ death, where the entire party is then surrounded by easily-killed, no-damage clones of him.
Blast: Point-blank AoE cone aimed at the highest-Enmity target. Deals moderate damage, but enough to one-shot a careless healer. Can also be used in the opposite direction the boss is facing, but then it has a two-second charge time.
One final gimmick to it, though, would be the massive HP pool. Every single time the boss used Theta, and the party would survive, the entire party acquires a buff: Echoes of Power. It’d increase the party’s DPS output by about 100x, but only for 8 seconds after Theta was used.
The boss/fight would legitimately end when the boss is defeated in the third phase. This is all subject to easy change, if it is even implemented in any way. It’s mainly an experience for the first people to kill the boss, not much past it.
PS: The Fiends would look so much like him, and if anyone had the boss as a Focus Target, when he summoned the adds, one random Fiend among the 15 would take his place as the Focus Target. The thing is, though, the Tank Fiends, the Deadly Fiends, and the boss would all have a FFXIV SLIGHTLY different tint and would act somewhat differently too.