The most bullcrap boss/es.

[IankBailey]

My favorite boss is the dual Rajang (Final Invitation) fight in Monster Hunter Freedom 2. Did that fight with double heroics and a bow, now that's a fight that demands perfection literally. If you get hit once even nudged you die. That's why I never understood why people thought Dark Souls was hard. Although I did enjoy the Sif boss fight, took him down at my friends house during my first 30 minutes of play but I guess spear and shield is a good build or something.

Dullahan, that optional boos form Golden Sun: the Lost Age. I mean, the three games' last bosses were exercises in "I've used HOW many potions?!?", but eminently beatable if you grind it out a few levels and pick up the best gear, with the fights just taking forever. Dullahan, on the other hand, just decided not to play fair. Though basically cut form the same cloth as most other "generic super-tough optional JPRG bosses" he had a few chep tricks that kept me snarling at my GBA for hours. Before I found a few guides he killed me way more than any other boss I had ever encountered up to that point.

If your curious there's a turn by turn guide for that fight. Takes 3 or 4 full turns for a guaranteed kill.

 

[Steel_crab]

Alma from Ninja Gaiden.

All of my hate. ALL OF IT.

 

[Polite Sage]

Capra Demon of Dark Souls comes to mind. Not because he is hard or anything (I have beat the game 5 times now) mind you, but because you're going to die with 100% probability the first time unless you possess clairvoiance or inhuman reaction time.
Enter fog gate > You have 2 seconds to dodge a one-hit kill attack (depenging on your vitality), avoid two dogs that staggerlock you AND run up a set of stairs behind the boss and the dogs. In a confined area with no escape.

And the two last bosses of Valkyrie Profile 1. They both have this 1-hit party dies kthxbye finisher, which can be only countered with an item that auto-resurrects your party members. Only, the item in question has a 50% chance of breaking every time it's used so the battles become luck contests.

The hardest no-bullshit boss fight would be Yakumo Ran from Perfect Cherry Blossom's Extra Stage. Took me exactly 99 tries to beat her (the game counts your retries). And there is still ONE MORE boss after her.

 

[Electrogecko]

Most annoying boss I've ever fought was Saren from ME1. His health bar went down slower than an old person's driving.
Hardest boss would be Boost/Spider Guardian from Metroid Prime 2. Those two can go straight to hell.

Oh my god I remember having absurd difficulty with the latter.....then even more on hard mode.