In Pokémon Red and Blue, there is a truck in a location that, under normal circumstances, becomes inaccessible before it becomes accessible. Its sprite appeared nowhere else in the game. Rumors told that using Strength to move it would reveal a Pokéball containing a Mew. This was a LIIIEEE.
Of course, RED only tried it because Oak told him that he'd give him five bucks if he filled out the Kanto Pokédex. By the way, I made a wallpaper for this.