I'm not sure of any 'revolutionary game mechanics', so I saved a favourite house rule from yesterday, because I think it's clever and adds and interesting element of chance to a game - and because it stemmed from an attempt to circumvent an attempt at "play to win".
It started in a D100 homebrew system (not sure of the setting: I wasn't in the game itself) where one player's dice were suspiciously good: rather than use a proepr percentile, he'd roll different coloured D10's, but declare which was 10's and which units after the roll had landed. To get past this, the GM decided to mix things up by sometimes seeking a high number, and sometimes a low number. And he wouldn't tell you which he was after until all results were in. It got more complicated: he split it into 4 quarters and you needed to land in (or pass) the right one, with your stat assisting your die roll. To increase the randomness, the GM would also roll a D100. Ostensibly, I believe, this was to determine which quarter the target was in, but there were added side effects that were fun and leaked into games I did play in.
If your D100 roll matched the GM, something very bad was about to happen. If, however, your roll was his inverted (eg he rolled 38 and you rolled 83), something very good would happen. If the GM's number was a double (eg 22) and you matched it, something very good and something very bad would happen.
Then certain numbers took on meanings - if the GM or a player rolled it (and we are strictly talking about the die roll, never the stat-manipulated result), then something would happen. I forget all of them, although one number resulted in something completely off-the-wall, 69 usually caused something unexpectedly, ahem, lustful, and 66 (as in Star Wars's 'Order 66') meant something very bad.
I think it's clear that can add fun to a silly game, but it was surprisingly effective in more serious games too.