What version of Tetris are you talking about

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Tetris & Dr. Mario does not save high scores. No battery save, so when you power off the console, high scores are wiped.

But there’s a hack you can apply (to the PAL rom) to make it save high scores!

www.romhacking.net/hacks/2344/

In the RetroPi config, there’s an option to Autosave when exiting a game, and another to Autoload on start. Combined, they help keep high scores around.

Just remember that if a game autosaves into a crashed state, you can recover by loading an old save, or by doing a reset in the RetroPi menu.