The Dreamserpent is a dragon that is cooked as a snack for the Fat Consul in How to Speak Dragonese. Dreamserpents are not mentioned again until The Complete Book of Dragons. No description given. Evidently it is edible though!
In The Complete Book of Dragons, Dreamserpent's feces are described: ''They can drift through the air, as light as cobwebs."
They are also listed as Tree Dragons in the back, in the Key to Dragons. The Key shows that they can speak both Norse and Dragonese. They also possess chameleon abilities (its not clear if this means they can change colors, or simply blend in with their environment. In addition, Dreamserpents have the rare ability to look into the future. Only Horrors and Seadragonus Giganticus Maximus dragons are known to be able to do this.
- How to Speak Dragonese (Book 3), Cressida Cowell. 2005
- The Complete Book of Dragons: Guide To Dragon Species, Cressida Cowell. 2014