Boss battels you've find infuriatingly diffucult but found out to be easy (possible spoilers!)

[Canadamus Prime]

Gi Nattak in the Cave of the Gi,FF7.
At the time I did not realise he was undead, and that a phoenix down/x potion would stop me having to repeat it 4 or 5 times.

I never found him all that hard, but he defiantly becomes a non-issue once you realize that all undead creatures in Final Fantasy, including bosses, can be taken out in one shot by throwing a Phoenix Down at them.

Now an boss form FFVII I did have a hell of a time with on my first playthrough was that damn demon door thing from that Ancient Temple.

 

[Eskwyre]

Shao Kahn. You have to duck the charges.

 

[Dalek Caan]

Ruddy bloody RAAM on ruddy bloody Gears of War on ruddy bloody Insane difficulty. Took the best part of two weeks to kill that bastard. Finally found out that I could glitch him out behind one of the stone blocks on the train and slowly shoot him in the head.

 

[jdogtwodolla]

Stupid Pirate crabs in Donkey Kong country returns because i was reading the pig sign as beat the ground instead of roll into them.

 

[Dark Claw13]

The final boss of Rayman 2 had you both over a pit of lava, and you had to hit his arms to drop him into it. This only took away a tiny bit of life, but what I didn't realize is you can continue to shoot him while he's down to do quite a bit more damage. I originally beat the final boss the very hard way.

But when you shoot him in the lava he shoots you right back.

 

[Gabriel Majeski]

Shadow of the Colossus... That entire game.