Back at Saturn Valley
Now that you have defeated Belch and rested in the hot springs, it's time to prepare for the next "Your Sanctuary" location, Milky Well. Remember that Mr. Saturn in the cave that said he'd give you an item if you defeated Master Belch? Go find him again and you'll receive a Mr. Saturn Coin. Equip it on whoever needs the most defense and luck.
Now check Jeff's IQ. If it is higher than 24, go rest at the hotel so that Jeff repairs the Broken Laser. If it is lower than 24, go outside and train until you can repair the Laser. Equip Jeff's new weapon as soon as you have it. You don't need the Jar of Fly Honey any more, so call Escargo Express and have them pick it up (as well as other items you won't be using).
Now head back to the hotsprings. There is a Mr. Saturn there that will give you coffee. Drink the coffee and you'll enter some sort of bizarre dream-like one-sided conversation. After you are done tripping out, head into the cave to the north of the hot springs. PSI Fire works well on the enemies here, so don't be afraid to use it. If you are mushroomized inside the cave, just head back to the hot springs to get rid of it. When you get the Coin of Slumber, have the person with the lowest defense equip it and then go fight the boss, Trillionage Sprout.
Once the Sprout falls you'll be able to record the melody of the Milky Well. On the way back through the cave, fight the enemies by attacking from behind to gain some more easy levels.