Yoshi is a Pokemon

On Pokemon Red/Blue you train a dragonair until its about to evolve, you go into the mysterious dungeon and the location were Mewtwo was. You use thunderstone and dragonair evolves into dragonite except his sprite is going to be of Yoshi not Dragonite.

That was the April Fools Joke of 1999 of some magazine. I remember reading it and thinking it was real, it seemed like an easter egg, its not like they were telling you how to get Mew or that Yoshi was a Pokemon, in fact they told you it was just a sprite change everything else was a regular Dragonite.