Very cool image and I really like the light/dark patterns you have going on here.
One thing I might suggest is really looking at how your compostion relates to your pose. Typically the front view is very limiting in terms of creating imposing shapes. This is because everything is seen in a foreshortened view. If you compare These images of buffalo (or any animal) you will see how informative the side view is and how it trumps the front view in terms of giving a clear silhouette to your characters. Now, of course you don't want to draw everything from the side view, but knowing that the side view is the clearest view can influence how your composition works.
With your composition here, using a good 3/4 view of the buffalo would be much better. Maybe have him coming around the corner or something. Then you can really get in there and draw those overlaps and big ol' shapes those creatures have.
So basically if a creature is much clearer from the side vs. front, I try to give them an angle to be shown from so it gives you a clearer read and gives you more that you can draw. I did a slight turn on your buffalo here just to show how much difference even a slight turn can make.
Hope that helps some. Can't wait to see this guy finished up! : )
