The Singetail is a Stoker class dragon introduced on June 24, 2016. One Singetail is rewarded as part of a quest of Return to Dragon Island Expansion. They can also be bought from the store for 750 gems (600 for members).
"Fiercely territorial, Singetails don't just breathe fire--they send it blasting out of their jaws, gills and tails.
First discovered by Spitelout when he colonized Storehouse Island, the elusive Singetails prefer to scare away their enemies with long-range attacks, like hurling fireballs from their tails. However, Singetails also pose a danger in close-quarters combat by shunting jets of flame from their gills lining their exposed underbellies."