My favorite hoaxes were that you could unlock Tabuu, Ridley, and Master Hand as playable characters in Super Smash Bros Brawl. There were so many troll videos where people would either mod their game or talk about how it was possible.
Here are two examples of videos [first] [second]
That second video was actually the first time I ever heard Caramelldansen
I think the strategy was that in order to unlock Ridley as a playable character, you had to beat Tabuu with Samus 3 times on hard mode. For Tabuu, you needed to beat the Subspace Emissary like 30 times on hard mode and have one million brawls. For Master Hand, you basically have to 100% the entire game.
It was obviously all a hoax but it was so fun to try and do. And then, in Smash Bros Ultimate when they made Ridley an actual playable character, I lost my MIND! I got so nostalgic for all the times I tried to unlock him in Brawl. And in Ultimate, you also get to play AS Master Hand for a moment. It brought me back so hard.