Well, I been working on this to see if it can be put in along with Freedoom, I admit I did use two sprites for ruff reforence but I don’t think it’s an exact copy. I might enter it into one there art contest as well, my goal is to get them into Blender.
The horns need to be thicker and coming more out of the side of the head. Also the shape of the legs needs refinement. You could use your donkey legs as a basic template for the bone structure.
I think the horns would indeed look better if the where thicker. And I think you should change their shape. Instead of this ‘wave’ make it one curve.
I suppose I can have them from the side, I see what I can do.
Well, here’s an update, I’m just showing the head, because that’s the only change, I’m sort of pondering on how to create the mouth thoe. Tell me what you think.
Definately looking better. To make the mouth you may have to add a couple of loop cuts in that area, then extrude the mouth region inwards.
Will extruding the bottom also work ?
My guess would be no, but you can always give it a try.
Ok, I put in a mouth, but I don’t really have reference on bulls, so I’m not sure about the lower jaw. Move some vertex as well. What you think ?
It’s too far in the middle. The top part should be bigger and rounder, and the bottom should be narrower in both front and side views, and fit against the upper part sort of like a foot fits in a shoe.
here’s a pic
I’m looking more for this type of image 
Some update, working on the hands and muscle, so much too this, what does everyone think so far ?