When I wrote music I sometimes remixed exsisting music. I also do this with game programming. Once I made a partial First person shooter combined with space invaders.
Yesterday I was thinking of thinking how I would combine the game asteroids and space invaders or turrican. I almost thought that the game pang was a combination of space invaders and asteroids. It is close I think.
Mixing or combining games might let you end up with new original games.