Electronic Gaming Monthly (abbreviated as EGM) is an American video game magazine published by Ziff Davis that started in 1989. It's one of the most popular gaming magazines in America.
Every April Fools' Day, Electronic Gaming Monthly does an April Fools' Day joke. One of the most famous is when they said that Sonic and Tails can be found in Super Smash Bros. Melee if the player completes a very hard task, and for a long time after that, people thought that they really were in. Sonic later appeared in Super Smash Bros. Brawl.