I don’t remember the name of it, but it was just a super troll hack where you’re presented with the normal game for Mario 1, but then every obstacle had a hidden obstacle that would kill you when you attempted to play it as if it was the normal game.
There was another game made around the same time that was built entirely on that premise, but I’m pretty sure the Mario hack came first. I at least played it before I ever heard about I Wanna Be The Guy.