The new boss in FFV:A (spoilers)

[Kawaii Ryûkishi]

That's just the boss rush--thirty bosses from throughout the game, broken up into groups of five that must be defeated in rapid succession. It's separate from the dungeon proper, only becoming accessible once you beat Enuo and get the Necromancer job. The sole reward for surviving it is another useless item in the tradition of the Omega Medal and Dragon Crest, called Proof of Crushing Evil.

First GroupWing Raptor, Garula, Siren, Magissa & Faltzer, Gilgame
Second GroupLiquid Flame, Sol Cannon, Purobourous, Minotaurus, Triton/Nergeid/Phobos
Third GroupBiblos, Tyrasaurus, Flying Dragon Weed, Archaeo Demon, Apanda
Fourth GroupChimera Brain, Adamantoise, Garkimasera, Calofisteri, Twin Tania
Fifth GroupHe Who Knows Everything, Stalker, Sand Worm, Atomos, Halicarnassus
Sixth GroupCrystals, Melusine, Catastrophe, Apocalyopse, Necrophobia

[Jowy]

That's just obnoxious.

[Zeromus_X]

(SPOILER)Who is this 'He Who Knows Everything', again?

[Jowy]

Playing the elimination game, I'd guess (SPOILER)Alte Roit

God knows I'm probably way off though.

[Zeromus_X]

Oh! (SPOILER)Azul Magia! Because he knows all Blue Magic. I guess.

[Kawaii Ryûkishi]

He's the guy at the top of the magic half of Fork Tower. His name is usually translated as "Omniscient," which is valid enough except that it fails to represent a minor pattern found later in the series.

FFV: He Who Knows Everything
FFX: He Who Has Surpassed Everything
FFX-2: He Who Has Abandoned Everything

[Evastio]

That's just the boss rush--thirty bosses from throughout the game, broken up into groups of five that must be defeated in rapid succession. It's separate from the dungeon proper, only becoming accessible once you beat Enuo and get the Necromancer job.

I hope the Necromancer Job will really help out during the boss rush.

[Sefie1999AD]

Great, so that means the new secret dungeon doesn't even end when you defeat Enuo. How are the pre-Enuo parts of the dungeon, i.e. navigating around, fighting battles, fighting bosses etc?

[Kawaii Ryûkishi]

It's a bit like the Dimensional Rift in that you move through different types of areas without much warning, but it's much more maze-like. You may find yourself running in circles before you find the means to progress, which themselves are usually unorthodox. You'll have to capture a particular kind of monster, run from one area to another within a time limit, and so on. Without saying too much, you're sure to love the pyramid segment.