You need to know both high jump (obtained in stardust fields) and mouse (obtained in Chataeu De Chucklechuck). Don't bother if you don't know both of these skills. Outside of battle, minimize Mario into a mouse and command Luigi to do a high jump. While he is in mid-air, command Mario to jump, hitting the bottom of Luigi. Luigi acts like a block, making a coin pop out from his head! Note: You can do this skill many times, but every coin decreases Luigi's health by 1. He won't die, but at 1 HP, you can't make anymore coins. Instead a short and funny scene will come up (i'm not spoiling it). If you are doing this coin skill, ya better keep some mushrooms or any HP healing item in handy.