The first legend that comes to MY mind is a folklore in Vienna. About the Basilisk(a snake-like creature with the head of a rooster and deadly poisonous breath). I can give you a (german) link: http://www.sagen.at/texte/sagen/oest.../basilisk.html, if that´s helping you.
Maybe it's based on Adam and Eve. The snake originally had arms and legs, but lost them after tempting Eve. Smugleaf loses his limbs as he evolves, so I thought it may be based off it, and have a grass/dark typing.