There is an interesting trick you can do in the original Super Mario Bros. when playing on real hardware. In this clip I am playing on an AV Famicom and have 1 copy of Super Mario Bros. and 1 copy of Tennis. To do this trick, you eject the Super Mario Bros. cartridge while the game is running and insert the Tennis cartridge. Reset the console and play a little bit of the Tennis game. After that you eject the Tennis cartridge and insert the Super Mario Bros. cartridge, reset the console and by holding A and Start on the title screen of Super Mario Bros. you will be warped beyond the intended 8 worlds of the game. In this clip I warped to World A but there are up to 256 worlds that you can theoretically warp to. https://famicomworld.com/workshop/articles/super-mario-bros-256-worlds/