Earthbound had a pretty fiendish one too, with the game not only increasing the difficulty of the main game by spawning extra enemies on a pirated version, but

Earthbound had a pretty fiendish one too, with the game not only increasing the difficulty of the main game by spawning extra enemies on a pirated version, but also wiping out your save data after it deliberately crashed at the final boss fight. Given that this was a 30 odd hour RPG, god help anyone who suffered from that one. There's also the infamous scorpion trick they did in one of the Serious Sam games too. If it detected the game was pirated, it'd load an invincible monster that could kill you in seconds and would hunt you down through much of the game. Certainly made for a memorable experience, though it may also gave a bunch of people the amusing extra challenge of trying to avoid the thing for as long as possible.