Even if you find the casino, you can’t actually enter it until you earn a membership card from Knife Guy. Once there, you can immediately enter Grate Guy’s Casino – as long as you’re cleared to, that is. From there, follow the path off-screen and you’ll pop back into the World Map. Defeat it, and then jump three times under the platform shown above to make it appear. In this new room, you’ll find a Golden Chain Chomp.
In the area with the Beezo and all the Piranha Plants, take the top pipe.
The path to Grate Guy’s Casino is hidden inside a pipe in Bean Valley, one of the later areas in Super Mario RPG.
