Here's why:
* Politoed evolves from Poliwhirl using a King's Rock. King's Rock is a held item, not a code or cheat.
* LeafGreen does not have an official way to cheat. There are no built-in cheats or code editors within the game itself.
* Third-party tools might allow it. However, using external tools to modify your game can potentially corrupt your save file, making it unplayable. It's generally not recommended.
The only legitimate way to obtain Politoed in LeafGreen is to evolve a Poliwhirl using a King's Rock. You can find this item in the following ways:
* Trade: You can trade with someone who already has one.
* Find it: King's Rock has a very rare chance of being held by wild Pokémon like Graveler.
Remember, playing the game fairly is always more rewarding and enjoyable in the long run!