1. "It's Possible to Jump Over the Flagpole in Super Mario Bros."
Ever since the "you can walk through a wall to access a never-ending water level" rumor proved true, Super Mario Bros. fans were willing to believe anything. One of the most persistent rumors was that it was indeed possible to jump over the flagpole at the end of one particular level. After weeks of trying, no one I knew was able to pull it off, and assumed it was false. It turns out that we just didn't know the right level to try. As this Internet tutorial explains, level 3-1 is just right for Mario to make a flying leap and land on the other side of the pole. After that, the screen just continuously scrolls to the right. Eventually, time runs out, like the pee that ran out of my pants the first time I saw someone do this.
2. "The Arcade Version of Galaga Has a Trick to Make the Enemies Stop Firing Forever"
Early arcade machines pitted computer engineers against quarter-starved hackers. Though modern games are designed to keep the gamer from playing too long without paying, several classic games could be played for insane lengths of time on a single quarter. Sometimes, this could be done with skill, like with people who play Berzerk until they drop dead. But sometimes, clever tricks allowed less-skilled player to capitalize on a hidden/not-so-hidden flaw, like trapping the centipede in Centipede, then shooting spiders.
The rumor sounded as ridiculous as every other pre-pubescent rumor I had ever heard: "If you play Galaga and leave two bees in the bottom corner of stage 1, then dodge them for 15 minutes, the enemies will stop firing at you forever." A lot of people I know tried this, but dodging the bees for 15 minutes proved to be a lot harder than convincing oneself the trick didn't exist. I had just assumed this was a rumor born from ridiculous verbal posturing on the behalf of an attention-deprived child. But then I saw videos of people doing it.
3. "The Sequel to Super Mario Bros. Wasn't Released in the U.S. Because it Was Too Hard"
Super Mario Bros. 2 was a black sheep of the Mario series. A lot of elements were unique to this game: The creatures were different, you could pluck useful items from the ground, Luigi was useful, etc. So, it wasn't surprising when a lot of gamer know-it-alls started claiming that the American SMB2 was just a re-skin of some other unrelated Japanese game. The reason was that Nintendo thought silly Americans couldn't hang with the increased difficulty level.
In 1993, Nintendo finally released the actual, original sequel to Super Mario Bros. in America, as part of the Super Mario All-Stars collection for the Super NES. This sequel was much more faithful to the physics of the original SMB; no word on why Nintendo though this was too hard, yet approved the stupid wind tunnel level from Battletoads.