In The Crystals, the caves are an optional side area. A tail collector in the cave will trade the player colored Tails for Small Tails, which can only be acquired in this chapter. Seven Small Tails can be traded for any colored Tail, but fourteen can be traded for a Rainbow Tail, the only way one can be acquired. Once the player can access the tail collector's home on the True Moon, these colored tails can be traded for rare items.