How do you get crazy frog in a Pokemon game?

Answer 1

"Crazy frog" is not a Pokemon, so unless you've hacked the game you can't get it in a Pokemon game.

If you're referring to the Pokemon Politoed, which does look a bit like a crazy frog, you need to trade a Poliwhirl holding a King's Rock.

If you're referring to the Pokemon Ludicolo, which also looks like a crazy frog, you need to use a Water Stone on a Lombre.