The Blubberwing is mentioned only in the beginning of "How to Ride a Dragon's Storm" through its fat: Viking use it to protect themselves from the icy cold waters of the Sea.
"Don't be a softy!" roared Gobber. "The Blubberwing fat you have rubbed all over you SHOULD keep you warm enough to prevent actual DEATH ... but its all part of the game of course."
Specifically, Gobber the Belch is referring to the Inter-Tribal Swimming Race. Later, Dogsbreath the Duhbrain dumps a "pot of slimy green Blubberwing goo" all over Fishlegs.
No description or information is given about the Blubberwing, though it might be inferred from its name that it is rather ... blubbery.
References
- "How to Ride A Dragon's Storm" (Book 7), Cressida Cowell. 2008