>>11797454There's a hack of NES Tetris that takes advantage of the MMC3's scanline counter to run the game's internal logic and input polling at steady frame rates other than 60 fps. You can set the game speed multiplier to any fraction comprised of only numbers 1 through 6. So 1/6 will run the game at 10hz (6 times slower than normal speed), 6/6 at 360hz (6 times faster than normal speed), and so on. This allows you to play PAL speed on NTSC consoles by setting the speed multiplier to 5/6, and NTSC speed on PAL consoles by setting the speed multiplier to 6/5. In the attached gif, my emulator is set to 50hz mode, yet the game plays identically to how it would if it was in NTSC mode since I set the speed multiplier to 6/5.
The 6x speed multiplier is only possible since Tetris is a very simple game that isn't taxing on the CPU. (At 1x speed, less than 10% of the frame is spent actually calculating logic. The rest is just the CPU spinning while waiting for the next frame to start.) The 6/5x multiplier would definitely be possible for most games though, considering the PAL NES has more CPU cycles per frame than the NTSC NES (29780.5 cycles per frame for NTSC vs 33247.5 cycles per frame for PAL).