You think the Castle is the best ending you can get? No way! Collect all of the treasures and get 99999 coins. Now beat the game. When the genie tells you to go look at your new property and Wario goes there, nothing is there. Then Wario will float into the sky until he gets into space. He will then land on a planet with his face on it! When all that stuff happens, you've gotten the best ending!

Note: If you got the castle ending instead, you probaly missed a treasure or didn't get enough coins.