Getting a boss battle just right is a tricky concept for many game designers. Often difficulty in general is something that depending on the genre you're playing, can amount to nothing more than the same enemies suddenly depleting a life-bar thanks to quadruple damage obliterating you in seconds.
There are others that totally nail it of course, and then there are those that sit somewhere in the middle; the games that you know in your heart aren't being fair and there's the feeling the designers put the whole thing together just to see how much you really wanted to get to the next level - and you know you've already spent way too much of the day trying to get past a certain obstacle. But there's something there. There's that quintessential 'thing' that makes you try again, and again, and again until you finally beat it.
Many a gamer has come out the other side of one of these experiences licking their digital wounds (or surveying the surrounding real-world damage) uttering various comments that all amount to the general consensus of "I am never... EVER, doing that again." You banished these creations from your mind and locked them away in a little mind-box you'd never need to look in.
Well, these are the nostalgia-ruiners, the roadblocks that actively laughed in your face and the ones that for many people are the reason they never even finished their respective titles in the first place. Buckle up, it's time to revisit the best of the absolute worst.