2002
Super Smash Bros. Melee's "Unlock Sonic and Tails" code, where players had to defeat 20 opponents in Cruel Melee mode. This prank went widely believed for months, to a point where rival magazine Nintendo Power had to create a blurb to try to explain the origin of the rumor while not indirectly promoting EGM by mentioning the magazine's name. After revealing the prank, EGM held a contest where those who sent in videos of their Cruel Melee battles with over 20 KOs would win a copy of Sonic Adventure 2 Battle.
In an interesting twist to the joke, the sequel to Melee, Super Smash Bros. Brawl, features Sonic as a playable character. In addition, Yuji Naka, the creator of the Sonic franchise, also admitted that he did consider implementing Sonic into Melee, but was unable to do so due to time constraints.
Read more about this topic: EGM April Fools' Jokes