Aside from size, the main difference between Draconis vipera and its larger cousin is that the former possesses only two legs, like an avian. Otherwise, it is quite similar, with armored scales, leathery wings, and the ability to spew projectiles from a pair of glands inside its mouth. The nature of these projectiles is tied directly to the color of Draconis' scales. Some spit fire while others unleash poisonous acid or even bursts of bioelectricity.
I can imagine no flying mount more deadly than Draconis vipera. Its strength, toughness, and ability to rain death upon one's enemies makes it unmatched in combat. The few creatures that it cannot immediately overpower, it can outmaneuver. In fact, it is puzzlingly suited for a life of servitude, despite being such a vicious predator. The ridges on its back form a natural saddle, to the point where many riders prefer to ride Draconis bareback. Curious indeed.
Like its relative from the island, the Draconis vipera that inhabit the aptly named Dragon Trenches are creatures straight out of European legend.