Yellow Vampire

Yellow Vampires are dragons mentioned once in "How to Speak Dragonese":"An enormous number and variety of dragon species were being held prisoner behind the bars of this cage. Deadly Nadders, Flying 'Gators, Big Spotted Gormlesses, Yellow Vampires, Common or Gardens - you name it, they were all there, trapped together in a furious tangle of talons and wings and fangs, ready to be sent back to the restaurants and shoemakers in Rome."This is what Hiccup saw after being captured by a Roman ship. Yellow Vampires are not mentioned again, nor is any description given. One theory is that Yellow vampires are a variety of the Vampire Dragon, which are typically dark in color.