1. Mewthree
As a child, this alongside Football was the only thing I ever really did and this rumour was without a doubt the number one in hearsay. At countless times, I heard that either Mewthree had been sighted in their game or that it was the to be included in the next Pokemon title. No of this ever came to be true, but there was more to this rumour than simple gossip. During the 90's kids around the world were convinced that there was a Mewthree somewhere in the world of Pokemon and that they had seen it. This rumour stems from the very beginning of Pokemon and is due to the origin of Mewtwo, being a clone of Mew. Since then, many have expected Mewthree to also be Pokemon and to have been inserted into the game and when glitches occurred such as the "Missingno" of Red & Blue, many assumed that this was the apparent Pokemon before it got scrapped. The truth to that is simply it was an error in the coding which was never rectified. The recent announcement of Pokemon X & Y has one again sparked a debate between the Pokemon community due to the reveal of Mewtwo being given a new form and if this new form is the long awaited "Mewthree", personally I doubt this as it is another 'form' and not a new Pokemon all together. For me though, this rumour topped the list for simply due to how viral this rumour went at a time where the world wasn't truly accustomed to the virtual world, and for myself at around 8 years of age to pick this up only signifies how largely this rumour had spread.