QFMFT. Spoilers for the End fight in MGS3, so don't read if you don't want to.
One of the longest, most exciting boss battles for me personally. I think I was playing for about two hours on that encounter alone before I decided to call up my friend (who had lent me the game in the first place) and ask him whether I was doing something wrong, or the battle was supposed to be this long. Well, as I call him I hear a slight breathing noise coming from the TV. I shrug it off, pause the game, and call him up. He tells me that, yes, the battle is supposed to be that long. As a passing thing before hanging up, I ask him why I'm hearing odd breathing noises. He then yells " THE END IS RIGHT ****ING BEHIND YOU! DIVE DIVE DIVE! I unpause and quickly dive, to see a bullet barely missing the top of Snake's head. I turn around, chase him, he gets an asthma attack, and cigarette gas spray the bitch to death. Now that I look back, I got so ****ing lucky in so many ways during that battle. His stamina was super-low at the time, he had an asthma attack, and I barely dived away from the bullet that would've made my two hours go to waste.
God, that was awesome.