They were indeed SNES Cartridges!
We wanted to add them as a little touch up to really drive in the retro theme we were going for.
Ingenious idea to use existing game and then reversing the roles. I enjoyed the game quite a lot. I would like to point out though that I had to deduce some points from inconsistent game mechanics were pipes and gun would not spawn when I intend them to. To make it feel better it should be more responsive to user input.
I can only echo what others have been saying about your game. It's highly repayable, really enjoyable and to top it off i had no issues with the game which is rare in a game jam. Only things i can think to critize is the fact that you cant return to menu after finishing or failing game.
Your game is really nice and i enjoyed playing it. However i found out it was hard to track where my ship was going due to its small size. Other than the minor hiccups here and there i appreciate the fact that you used a color palette in your art. It made the whole atmosphere breathtaking.