Message from Night
Mr., there were no gnomes, elves, hydras, or drakes in the world, so we can safely say that all the creature models in all the Heroes games are incorrect!
Dragon - a winged creature covered in scales, breathing fire (similar to a snake or lizard)
Cerberus - a hellish dog with three heads;
Angel - a creature similar in form to a human with wings, a messenger from heaven;
And many others...
Artists are already taking on their modification, and in fact, there are many variations;
In Heroes 5, you can also say that it's an exclusive opinion of the developers on how these creatures should look.
P.S. Don't you, Night, like how hydras look? And what is a hydra in your understanding?