|“||One hunting dragon went down in a blaze of flames, a Monstrous Nightmare belonging to Very Vicious the Visithug that sank its teeth into the neck of a much larger Grimwing, which then grabbed it around the throat, and snapping, biting, screaming down they went, doomed, into the Gorge in a somersaulting ball of fire.||”|
|— How to Steal a Dragon's Sword|
The Grimwing is mentioned once in How to Steal a Dragon's Sword.
There is no description of the Grimwing, other than what might be inferred—that it is a largish dragon, possibly a Mountain Dragon like the Razorwing and Tonguetwister it was accompanying, and had a strong dislike for humans.
The Grimwing was part of the group of Red-Rage dragons attacking Hiccup and the other young Vikings on the cliffs at the Gorge of the Thunderbolt of Thor while climbing to Flashburn's School of Swordfighting. Other dragons that were part of the attack were: Razorwings, Doldrums, Tonguetwisters, and Vampire Ghouldeaths.