What is the most difficult boss/challenge in your favorite game?

[Glongpre]

Hmm, in Ninja Gaiden Black the hardest fight is Alma Awakened. She just has really good defence and her grab attack does a ton of damage. She requires lots of movement and is just quite solid, no real weakness in her offence or defence.

Spoiler: alma awakened

I think this captures the difficulty well.

 

[IllumInaTIma]

First encounter with Imaginary Numbers in Front Mission 3. So, you and your team are going across some underwater tunnel and suddenly 4 torpedo breach through the windows! Oh my god! Who could that be? Oh. It's just 4 guys in some weird wanzers, nothing scary, I was able to beat 10 and more wanzers in one fight. Battle starts and suddenly these 4 guys simply annihilate your entire team. That was terrifying.

Also, Contrarian King, bonus boss in Yukiko's dungeon in Persona 4: Golden. Unless you're overleveled, that guy will bitchslap you to death, literally!

 

[IpunchFaces]

The Horsemen in Shin Megami Tensei: Nocturne.

Holy fuck. What an absolute kick in the balls.

 

[waj9876]

Steambot Chronicles.

The hardest boss fight? The champion of the trotmobile tournament who is also the final boss in disguise. You aren't expected to win that fight, hell, you aren't expected to win any of the fights in the tournament, and you probably won't win most of them on your first playthrough.

But man, that White Phantom guy...he has the hardest AI in the game, the best melee weapon in the game, a pretty fucking good ranged weapon, and the only really good strategy for him doesn't work sometimes. Like, at all. Being too light means you go down too fast to do anything, and being too heavy means you take a ton of hits before you can get in close. It requires balance.

I've only beaten him like, twice. And I've played that game a lot. A lot.

 

[WhiteFangofWhoa]

Omega Pirate from Metroid Prime. One telling factor is that the most in-depth walkthrough for the game on GameFAQs gives every boss before him a difficulty rating of 5 out of 10 or lower... then Mr. Omega gets a 10 outta 10.

You're used to dodging colossal-sized Pirates who unleash shockwaves and energy blasts from their shoulder canons at this point, but doing so in a cramped room where half the floor is covered in lethal Phazon is quite a bit tougher. He also requires much more precision aiming than his brethren, and once you've destroyed four fairly durable targets on his body (2 Super Missiles each on Hard!) then you can start actually damaging him...

And then he goes invisible, teleports over to one of the Phazon pools to regrow his armour in about 30 seconds, AND summons various Elite Pirates (all of whom have big hitstun attacks and are weak to von und precisely von beam at a time) to make you miss your small window of opportunity to hurt the big fish. This guy would be the bane of a minimalist run.

The first phase of Metroid Prime itself may also count on Hard mode simply due to how much stamina it possesses and how much damage all of its attacks do by comparison to yours. It's like you being able to take 80 hits, and it being able to absorb 8000 with a constantly shifting weak spot that is hard to hit with the Ice Beam. It gets boring sometimes TBH, but that doesn't make it any less dangerous.