In Pokémon FireRed, LeafGreen & Emerald, lies a cave named the Altering Cave. At first glance, all it has are wild Zubat, which makes me people ask "why the heck does this cave even exist to begin with". As it turns out, there is more to this cave than it meets the eye. This cave was programmed to make use of special Mystery Gifts, that would allow the wild Pokémon species present to be altered. (The species present changes every time one talks to the deliveryman) Sadly, this game