Aromatherapy diffusers come in all shapes and sizes and serve multiple purposes. The one in Animal Crossing: New Leaf appears to be a clay or ceramic pot. The idea is to place oils, herbs, or spices in the pot and have the smell spread in the air. Some involve using a candle, much like burning incense. The uses can range from helping with sinus problems, to making your room smell a certain way. Some have patterns on the outside, so when the candle is lit inside in a dark room, it will not only make your room smell nice, but it will leave pretty patterns on the wall!