oh, FF8. Omega was my ceapest victory ever. I fought it for ages, then gave up and used that thing where you start spelphie on a limit break and lift the cover. It just kept repeating her choose a move again and again untill I managed to stop at "The end" her insta-kill move. I'm ashamed.

Gundam: Battle Assault 2. I just picked the Dark Gundam or whatever it was called and just kept spamming its entire screen unblockable move. I beat survival mode literally with my eyes closed.

Do not be ashamed, for I did the same thing! XD

In Tekken if I was desperate I would cheat using the character's one move over and over again, making them have no chance in fighting back.

Tekken Tag Tournament: teaming up Roger the Kangaroo with the Devil. Lead off with Roger's wind up punch that knocks the opponent accross the screen and reduces them to a sliver of life, then tag in Devil and immediately fire off the eye-beams that hit everything on the screen. Victory in about 5 seconds. Eventually, people started realizing they could hit me while Roger was winding up, and so the strategy stopped working after a while.

Still, the dirtiest trick I've played was just a couple days ago on World of Warcraft. I was running around with a couple guildies (a hunter and a warrior, as well as myself as a warlock) and 3 or 4 alliance players show up and start PvP flagging themselves and taunting us. Now, I was pretty sure we could take them because the warrior and I were both at level 39 and they were all only in the low to mid 30s, and I had formulated an elaborate plan of attack, but then the warrior says that we should just wait for his wife to show up on her lvl 48 druid. Well, I felt that waiting was for suckers and just used my Ritual of Summoning spell to teleport her right on top of them and immediately attack. Those lighties were dead before they even knew what hit them.

It was a dirty, dirty trick, but too funny to resist. Besides, they were asking for it!

I don't remember any pure luck victories, but I do remember my worst defeat...
I was beat @ Dance Dance Revolution, during E3 a couple of years back @ the Konami Booth, ...by a guy on crutches. That was the last time I played...

KotOR II, making the place a mine trap to kill off the twins. Cheap me!

Lord of the Rings: The Return of the King, I used Gandalf's Magical Shield to kill the Mouth of Sauron (running around with the shield on damages enemies and knocks them down at the same time, plus it a super easy combo)

I also completely nuked an enemy base to oblivion once in C&C Generals: Zero Hour.

In final fantasy 8, I defeated Sifer in the battle in the Lunatic Pandora in ten seconds with Odin - it seemed somewhat off.

If I recall, in Mortal Kombat - all I'd do was use Scorpion (or his equivalent in the game) and use his grappling wire followed by repeated uppercuts.

In KoF I just learned one desperation move and use it as many times as possible before I'm killed.

You sure odin killed sifer? Thats odd. Very odd.

Oh, and I used mines to kill the twins in KoToR to, they were tough, and I'd only just made the guy a jedi.

Yeah, I'm pretty sure Seifer killed Odin and not the other way around. Then Gilgamesh showed up at the end and finished Seifer off.