most damn hard/macam **** bosses for me:

KOF2001 - Igniz
man, almost, almost impossible. win it by luck, 2 times. forget what difficulty setting I used that time.

KOF XI - Magaki
another hell. never win this. his pink color attack seems impossible to dodge.

Half Life 1 - that-final-boss-with-big-brain
using no gravity cheat to win this. after 2 months struggling.

yoshi Island - the-final-dinosaur-in-final-level
lotsa money wasted buying batteries (1st batch of GBA) . really hard to estimated where to land.

doom 3 -final
i reserved so many weapons just to kill it and wasted not using it.

Pokemon Silver/Gold/Crystal - Ash/Satoshi
after beating all 16 gyms, both johto/kanto elite four, still no match to fight ash in silver mountain. Pikachu alone can zap all party. never win this (to lazy to train, even elite four seems so kacang.