The eye of a Giant Deathwatch is the only mention of this dragon, as seen in the Complete Book of Dragons. No description is given, though it must be pretty big due to 'Giant' being part of its name.

Interestingly, in How to Speak Dragonese, when Camicazi and Hiccup meet for the first time and sword-fight, Camicazi uses as sword technique called the Deathwatch Parry.