I used a recipe I've adapted from the Vegetarian Resource Group, which you can find on my old New Leaf Vegan Society blog. It's a sturdy, very tasty gingerbread recipe that has oatmeal and some orange zest in it. The recipe is very to make and work with. A single recipe of the dough will yield a herd of about 12 bison...depending on how thick your dough is and how large the cookie cutter. The one I used is roughly 3"x5". After mixing up and chilling the dough, cutting out and baking them, I iced the wooly beasts with this:
1/2 cup powdered sugar,
2 tablespoons cocoa,
1/2 teaspoon vanilla extract
pinch of salt
about a tablespoon or two of water.
I just stirred this up in a small bowl until it was the consistency of a thick ( vegan :) ) cream. You can add more water or sugar as needed. Then I spread some on the bison with a small offset spatula, starting at the head and dragging towards the tail. While the icing was still very wet, so the next things would stick, I set in a toasted almond sliver for the horn and chocolate sprinkles for shagginess.