Fan-made, free-to-play online game which it drops 75 players into either world 1, 2, or 3 from Super Mario Bros. for the NES. In order to win, you have to be one of the first three players to reach the castle at the end of the world.
While you can't directly impede the progress of other players (who are represented by a "ghost" effect) just by running into them or around them, it is possible to utilize power-ups like stars to knock out the competition....