Hah cool idea for a thread.
Noel Berry and I made a game this weekend at a game jam, it was 9 games in 1 where once you beat a game, you could "scroll" the screen over to one of the other games, and the goal was to beat them all.
For example, there was this weird duck hunt style game where you have to shoot the white duck:
But when the duck game ended, we forgot to remove the rest of the ducks, which are instructed to just fly around on the screen. So when we scrolled over to the next game... guess who followed the camera:
We thought it was such beautiful bug we decided to keep it in as a feature.