Leaf Stonein Pokémon Polished Crystal

Evolves certain kinds of Pokémon. The Leaf Stone evolves quite a few Pokémon! You can get a Leaf Stone from Bill's grandfather if you show him an Oddish. They're also found in various locations and can be purchased later in the game. Leafeon being available via Leaf Stone instead of location-based evolution is a really nice quality-of-life change than being in a certain location only.