Earthbound is notoriously difficult to emulate accurately, partly because the cartridge had a unique chip on it used to detect if the code was running on an authentic cart, for piracy detection. The game will run a check on this chip to read its voltage; if it's not at the correct reading or if it returns a null value, the game would know it was running on a bootleg cartridge.
What it did then was kinda sinister. It didn't stop you from playing the game. But it GREATLY increased the spawn rate of enemies, making the game significantly harder. Then, if you managed to make it through the antipiracy hard mode and get all the way to the final boss, the game would intentionally crash itself as soon as the battle begins, and it deleted your save file. You couldn't finish the game. It let you get 99.99% of the way there, uphill, and then says "get bent" and wipes all your progress.