>>41880970As someone who thinks fan theories are retarded, the Gengar one does have some merit. Ken Sugimori designed both Clefable (Clefairy was his response to Pikachu by Atsuko Nishida) and Gengar. Both its English and Japanese names are shortened corruptions of doppelganger. It's meant to be a shadow, a dark copy of something, and its shape roughly matches Clefable. Do I think that it is literally created from Clefable and tied to it in lore like Shellder and Slowpoke? No, I think it's just mimicking its shape. Gengar was created long before Clefable though, and its original sprite isn't as distinctly shaped as its art. It's a bit more amorphous, almost like a stout fuzzy blob. The similar shape to Clefable may have been a decision later on when Sugimori finally began doing the official illustrations for each Pokémon. In that case, he probably did it as a personal touch without putting too much thought into it. After all, a lot of Pokémon like Venomoth and Koffing got notable redesigns from their original sprites.