The most difficult part of a deer is, of course, the antlers. The deer itself looks more like a horse, just with a head of a slightly different shape. But the antlers—they're really something!
First, they have prongs that stick forward. Then long prongs that stick backward. And from these, smaller prongs stick out in different directions. I figured it out with great difficulty. Try first to sketch them with simple lines. This will make it easier to understand the form.