3 bosses that are harder, since that is pretty much just memorizing a pattern.
Star Ocean 2 The Second Story Iselia Queen.
You pretty much need to be level 255 to beat this boss, which is crazy enough already (making it harder)
[ame="http://www.youtube.com/watch?v=S_10qwJP3-0"]http://www.youtube.com/watch?v=S_10qwJP3-0[/ame]
Again Star Ocean 2 (though you could take the final bosses from any star ocean game) boss name is Gabrie Celesta. you do not need to be such a high level, but that is a very tough fight.
***Language Warning***
[ame="http://www.youtube.com/watch?v=UCHZCGMq-1w"]http://www.youtube.com/watch?v=UCHZCGMq-1w[/ame]
third and definitely not the least. i couldn't find a video for this one, don't know if it exists. but there was this video game for sega genesis back in the day called terminator vs robocop and my cousin and i rented it once. we slapped on the cheats and our turbo controller and went to town. it was a really fun game but then we got to the last boss which was just this giant skull. we had god mode and infinite ammo with all weapons, and the best weapon for this guy was a gattling or mini gun type of thing. and this boss flies around and shoots out enormous amounts of stuff but just so we could say we beat the game we tapped down the shoot button on our turbo controller, aimed robocop with his mini so that he always hit the boss and waited.
it LITERALLY took 45 minutes, give or take a couple due to memory, to kill this thing. we both still remember it and both still think it is absolutely impossible to beat that game legit
PS. that boss does look insanely hard, i did not mean to sound like i was down playing that boss. that game looks really awesome too btw. i love and wish i still had Raptor