Goreblaster

The Goreblaster is mentioned only once in "How to Fight a Dragon's Fury", as Big-Boobied Bertha reminisces of home during the Dragon Rebellion.

"Sadly, Bertha, Chief of the Bog-Burglars, sharpened her axe, looking back at happier times when she was striding waist-deep in the delightful bogs of home, her faithful Goreblaster swimming by her side."

This passage implies a Goreblaster might be classed as a Bog Dragon, and used as a Hunting Dragon. Because the dragon is swimming while the human is wading through water, it is probably around the size of a dog.

Another possibility is that the author meant to reference the Gorebluffer, a dragon assisting humans (Alvin the Treacherous and Excellinor) in Book 11.