One of these days I should dig through my old cards. IIRC, my last tournament deck was pretty tight and vicious. Had exactly 40 cards in it (the tourney minimum) and used pestilence to wipe out opponents and their creatures. The deck which beat it in the last tourney I was in was a very well crafted all blue deck (and he beat me in the final round).
I can't remember the complete details, but it was black and white. It had nothing but smallish regenerating black creatures, and white knights (both types at the time), with protection from black. It had 4 pestilence cards, and some circles of protection: black. It also had a few nasty uncommon and rares in there just to keep people on their toes. The whole plan was to get pestilence out along with a creature or two that couldn't be killed by it. Get the circle out as well and the game is basically over. Any creature on the board is dead, and damage is constantly being done to the other guy. Mana was a bit tight, so it usually required 4 or 5 points each round, but most decks just couldn't do anything once the combo was out.
In the semi-final of that tourney I did beat a really tough blue deck (blue was difficult to deal with due to this decks vulnerability to denial effects). I don't know if I was the first player to win a tourney game after losing all his hit points the round before, but I had to have been one of the first. I wasn't able to get both circle and pestilence out before he got a ton of creatures and was going to blow through me. All his damage was done during the main round though, so I let him through (saving my creatures), let him do massive damage to me during the combat putting me at negative hps. Then I cast simulacrum and directed all the damage I'd taken since the beginning of the main phase onto a poor wee skeleton...
Then I hit him with a round of pestilence, started my turn, and finished him off with another round of damage. It was fun. ;)
I think that was the same tourney where I actually felt sorry for a kid I was playing against. He had an all black deck. Lots of completely vicious cards and creatures. He didn't actually understand what protection did and had to call one of the mods over to clarify the rules. He almost started crying as he realized there wasn't a single card in his hand or in his entire deck which could do anything to me at all. Not only could he not do any damage to me, nor damage most of my creatures (much less kill them), he couldn't block about 2/3rds of them either. And his deck didn't include any method to get rid of enchantments. That wasn't nearly as much fun. I just tried to end it as quickly as possible and wished him luck on his next attempt.
That was right around the time that token creature generating cards appeared in the game. Needless to say, they didn't do well against that deck either.