Gengar and Clefable have, through trademarking and beta art, been proven to have been some of the earliest Pokémon made. (Coincidentally, they are also some of the first Pokémon when you list the original 151 by index number, with Gengar appearing shortly after Clefable.) Also, Clefairy was originally going to be the mascot of Pokémon (instead of Pikachu), so it was going to be a pretty important Pokémon. Have you ever tried to hit your shadow?