Earthbound Cheats

You can use the Rock Candy in battles an unlimited amount of times to increase your stats. You have to have it in one of the two very bottom spaces of one of your characters' inventories, and you have to use it with any condiment (preferably something like Sugar Packets or Jars of Delisauce, because they will increase one of your stats by 2 instead of one). This will allow you to get greater boosts in stats when you level up.

Note: This only works in the Super Famicom version of Earthbound(Mother 2).
In Mother 2, you could use the Exit Mouse in the Cave of the Past, which was never intended obviously, since the feature is missing in Earthbound.