Simply put, the RNG system is used to manipulate your chances of receiving loot, and the quality of said loot. It's used in Golden Sun to aquire loot from fights, the Lucky Fountain in both games, and in The Lost Age for blacksmithing. Most often, the RNG system is manipulated through combat. With this handy trick, you won't have to leave the fountain. Just cast a small selection of spells for the desired results, accessible from the menu. I suggest Ply. The tactic's baseline proceeds as follows... Put ply on a Hotkey. Stand on the Fountain's platform, with the water drained, ready to throw.