I once came up with a game genie code for a game in 15 minutes. My then-girlfriend (high school) called me up on the phone and wanted help because there weren't

I once came up with a game genie code for a game in 15 minutes. My then-girlfriend (high school) called me up on the phone and wanted help because there weren't any game genie codes that did what she wanted. The answer these days is emulation & memory search. Memory search gets used for hacking native PC games these days too although it's a lot harder when anti-cheat is involved. You give it a query like "show me values that decreased since we started observing" and you repeat the process to winnow it down to a memory location or set of locations. You then try fixing the memory location to a value and see what the game does. Incidentally, in Link to the Past, the heart containers are denominated in units of 4, which can throw you off. Going from 4 hearts to 3 means the value goes from 16 to 12. If you went down to 3.5 hearts it'd be 14.