Pokemon Red & Blue - How to get Pikablu!!
In order to get this exciting hidden Pokemon, you must train a Raichu to level 99 (without any Rare Candies!). Once you have done this, leave your Raichu with the day care couple. Defeat the Elite 4, and return to the day care. They will inform you that your Raichu has run away, and replace it with a level 100 Pikablu!
(There were countless versions of how to get 'Pikablu', this is the one that I heard (and fell for). Can't think of any original ones myself right now... but I thought this actual circulated rumour was funny enough.