If you can tell me any harder bosses than professor nakayama then please tell me, because nakayama is by far the hardest boss i've ever done. I posted this video of killing him, beware of the epicness btw.

http://youtu.be/qt2Q0fKueHc

yeah i know! Crazy, innit?

Anyway if you could send me a harder boss thnx.

Idk if that goldfish in that worm game is harder or not.  

Try beating Silver in Sonic 06  

Some of the World of Warcraft raid bosses are insane,

Usually it's a 25-man team against one boss and even then the most recent ones released have only been defeated by five guilds  

God of War 3 on Chaos Mode is probably the most brutal and time consuming difficulty known to man. Bosses are like the Hulk combined with a God.  

release Dominus on Hardcore Merciless difficulty in Path of Exile
if you die, you lose a few hundred hours of gameplay
was incredibly hard to beat and had me using the Alt+F4 killswitch numerous times  

That one thing in the cave on Graal Zodiac. Still haven't killed it.

I want to include that Borderlands 2 DOES have some pretty hard bosses (in the second campaign) in the DLCs. I wouldn't say they're excessively difficult, just time consuming if you aren't prepared.  

Any boss in Zelda II

Or Dark Souls  

Darlene the Witch in IMO TWOM.  

Shandra Manaya in Tera Online back when it was actually hard. Took almost a month before anyone beat it. Probably took me dozens of attempts before I cleared it, and that was with an experienced group.  

Moldorm. fkn troll.  

Sephiroth in KH2 on proud mode is a challenge if you aren't prepared.  

Dust2 boss  

Posted by eko

Dust2 boss

Don't rly have a boss but to add to this answer I have a certain players
Spundg and Yam on inferno was a pain in the ass to play against
and James on dust2 was insanely hard to try and do anything with  

Graal Babies 0-0  

Posted by Cutieno

Graal Babies 0-0

Alexmo? I need you to see this.