Super Mario World for the Super Nintendo is literally 24 years old... surely there isn't anything new to discover in it? A group of American gamers have managed to do something amazing using a bug in the game, and managed to program a game-within-a-game, without actually hacking the game ROM itself.
Check out this video - the action begins at about 31:55.
What they've managed to do is get the game to - at a certain point - trigger an game-within-a-game of either Snake or Pong.
To explain a little more - Pong and Snake are not built into Super Mario World, but they've managed to program them into the game. Whilst this would be relatively straightforward for a sufficiently talented hacker who can plug the digital file on the game cartridge into their computer, what these guys have done have programmed the game in-situ, using simulated button presses on the controller the send the program into the game.
If I'm understanding this correctly (which I admit, I may not be), the exploited bug in the game essentially enables the player to execute arbitrary code (rather than the code the game makes the SNES run), and this can be programmed with the controller. To do this, as they say in the video - they hacked together a special cable that is the equivalent of a multitap plugin, giving them access to the full available bandwidth for uploading code - and then sent the code (using a computer) to the SNES in the form of button presses... so imagine entering an "up, up, down, down, A, B" style cheat code that is long enough to program an entire game.
And all of that effort to play Snake on a game that's not only old enough to drink legally, but is probably too old to be a professional footballer.
Seriously, watch the video - it'll blow your mind.