While the chocolate is still soft, press two pretzel pieces into the top edge of each cookie to create antlers. Below the antlers, add two mini candy eyeballs and a red M&M for the nose. Be sure to place the M&M logo-side down.
Repeat this process with all of the cookies, then let them set and harden in a safe area. Once the chocolate has hardened, use the black decorating gel to draw a small mouth on each cookie. Allow the gel to set.