Here's another one of these. I wasn't as happy with how this one turned out, but perhaps I can think of it as a rough draft for later improvement.
This, of course, is the ever-popular catoblepas, with its impossibly spindly neck and lethal breath. Many of the creatures featured in medieval bestiaries were based on garbled accounts of actual animals, and it's been proposed that the catoblepas is based on the gnu or water buffalo. With its heavy head and downward gaze, it can be considered an avatar of sloth, but like all venomous monsters I imagine it's mostly just pining for company.