Traits

There is no maximum limit on tail length. However, your dragon’s tail must be long enough to be able to touch the ground. Legs will not attach to the tail. When selecting species for a tail reference, do not mix them with other species.

You may use the tail of any water-dwelling species. The tail should only have one fin, and that fin will always be on the end of the tail. At least a small part of the tail will have a bony section—the end fin will not attach directly to the body. If you choose a species that does not live completely in water, then the tail should have specific adaptations to moving through water used in that animal's daily life.

How can I get multiple tails?
The split tail mutation.