Drecker
Smash Ace
Name who you think are the hardest boss battles in gaming, whether it be from amount of time taken to kill them, the fact that one mistake will lose a fight, or just the insane steps you need to take to beat them.
Rules
My nominations:
Boss: Matador.
Game: Shin Megami Tensei 1.
Why?: Simple: Shin Megami Tensei 1 is one of the hardest RPG's ever, and the only way to beat Matador in the solo encounter is by getting incredibly lucky with massive chain-crits, or else he'll just two-turn kill you.
Boss: Penance.
Game: Final Fantasy X International.
Why?: First of all, PAL only boss, you can fight him after killing ALL the Dark Aeons.
The preparation for this boss takes days, getting all characters to 99, all Celestial Weapons, getting Tidus's true Ultimate Overdrive, Finishing Blitzball to maximize Wakka's attacks (Unless you use Auron and have the fight take twice as long). It's ********, not to mention you need to chain the sphere grid with max ? Spheres to be able to get the max stats you need, getting auto-Haste and auto-Phoenix on all your gear, collecting enough Megalixers, etc, etc. The prep is ****ing stupid.
Once you can actually fight the boss, he takes around an hour (At least) of perfect execution to beat. Following perfect patterns so his arms never attack (One arm attack = You die), knowing when to kill them so they'll revive on a turn that you can attack them, and the boss having 15,000,000HP all make for a retardedly long, intricate fight. The hardest boss ever created by Square, no question. One mistake, and you will die to the arms.
(I KNOW IT'S NOT THE RIGHT PICTURE)
Boss: Dark Magus Sisters.
Game: Final Fantasy X International.
Why: The Dark Aeons are a feature unique to the PAL version of FFX. Once you get far enough into the game, you can complete specific challenges to fight "Dark" versions of your summons. The Dark Aeons typically have millions of health (Other than Penance, Anima has the highest by herself), and you will get ***** by them without certain stats and abilities. Auto-Haste, Auto-Phoenix, Triple Overdrive, Damage Break, etc. Not to mention you are required to have all the Celestial Weapons to do **** to them.
Naturally, the Magus Sisters, as the final Aeon, are the hardest (Anima is a ****ing joke, Bahamut is a ***** though). Dark Aeons hit for upwards of 10k on basic attacks (They all have damage break), reaching into multiple 10k's on specials. Dark Magus Sisters have so many ways to instagib your party it's ********. Bad Passado? You're dead. Bad Camisade? Probably dead. Let them get to Delta Attack? Game over, no question. Again, precision and patience are your friends.
Honorable Mention: Angra Mainyu (FFX-2).
Why? If you fight Angra at the right time (Before you can cheese the fight), it takes 4-6 hours. My friend Sean left the game on autoplay with a turbo controller with two Deathknights and an Alchemist on pure DPS / Heal rotation with near complete stat nullification, and came back three hours later to see he was dead. We later found out the boss will randomly solo-flare one party member for a oneshot. It's not hard once you figure it out, but it's INCREDIBLY long, seeing as you get one attack for every three heals and debuff removals.
Rules
- No low-level challenges (Round 2 Gilgamesh with lowest possible level in FF12, low-level battle vs Rufus in Disk 2 of 7).
Use of "Tricks" will not disqualify a boss (Yojimbo makes every FFX boss one-shottable).
Naming the FF7 Weapons makes you gay.
My nominations:
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Boss: Matador.
Game: Shin Megami Tensei 1.
Why?: Simple: Shin Megami Tensei 1 is one of the hardest RPG's ever, and the only way to beat Matador in the solo encounter is by getting incredibly lucky with massive chain-crits, or else he'll just two-turn kill you.

Boss: Penance.
Game: Final Fantasy X International.
Why?: First of all, PAL only boss, you can fight him after killing ALL the Dark Aeons.
The preparation for this boss takes days, getting all characters to 99, all Celestial Weapons, getting Tidus's true Ultimate Overdrive, Finishing Blitzball to maximize Wakka's attacks (Unless you use Auron and have the fight take twice as long). It's ********, not to mention you need to chain the sphere grid with max ? Spheres to be able to get the max stats you need, getting auto-Haste and auto-Phoenix on all your gear, collecting enough Megalixers, etc, etc. The prep is ****ing stupid.
Once you can actually fight the boss, he takes around an hour (At least) of perfect execution to beat. Following perfect patterns so his arms never attack (One arm attack = You die), knowing when to kill them so they'll revive on a turn that you can attack them, and the boss having 15,000,000HP all make for a retardedly long, intricate fight. The hardest boss ever created by Square, no question. One mistake, and you will die to the arms.

(I KNOW IT'S NOT THE RIGHT PICTURE)
Boss: Dark Magus Sisters.
Game: Final Fantasy X International.
Why: The Dark Aeons are a feature unique to the PAL version of FFX. Once you get far enough into the game, you can complete specific challenges to fight "Dark" versions of your summons. The Dark Aeons typically have millions of health (Other than Penance, Anima has the highest by herself), and you will get ***** by them without certain stats and abilities. Auto-Haste, Auto-Phoenix, Triple Overdrive, Damage Break, etc. Not to mention you are required to have all the Celestial Weapons to do **** to them.
Naturally, the Magus Sisters, as the final Aeon, are the hardest (Anima is a ****ing joke, Bahamut is a ***** though). Dark Aeons hit for upwards of 10k on basic attacks (They all have damage break), reaching into multiple 10k's on specials. Dark Magus Sisters have so many ways to instagib your party it's ********. Bad Passado? You're dead. Bad Camisade? Probably dead. Let them get to Delta Attack? Game over, no question. Again, precision and patience are your friends.
Honorable Mention: Angra Mainyu (FFX-2).
Why? If you fight Angra at the right time (Before you can cheese the fight), it takes 4-6 hours. My friend Sean left the game on autoplay with a turbo controller with two Deathknights and an Alchemist on pure DPS / Heal rotation with near complete stat nullification, and came back three hours later to see he was dead. We later found out the boss will randomly solo-flare one party member for a oneshot. It's not hard once you figure it out, but it's INCREDIBLY long, seeing as you get one attack for every three heals and debuff removals.