Melt your peanut butter, shortening, and butter together in a large bowl, then stir in both sugars and the egg. Whip everything together until it is completely smooth and fluffy, taking a moment to appreciate the warm, nutty aroma filling your kitchen space.
Whisk your flour, baking soda, baking powder, and salt together in a separate medium bowl. Gradually add this dry mixture into your creamed peanut butter base, stirring gently until it forms a soft, cohesive cookie dough.
Cover the bowl tightly and slide it into the refrigerator to chill for about 2 hours. This step is completely essential to help the dough firm up, which keeps the cookies from spreading too quickly and ensures your little reindeer hold their shape perfectly in the oven.
Preheat your oven to 375°F and begin shaping your chilled dough into 1 1/4-inch balls. Space them 3 inches apart on an ungreased cookie sheet, gently pressing them down to flatten slightly.
Decorate each cookie face immediately before baking by firmly pressing two mini pretzel twists into the top for antlers, two chocolate chips for the eyes, and a festive M&M or Red Hot right in the center for the nose. Bake for 9 to 10 minutes until the edges turn a light golden brown, let them rest on the warm sheet for 5 minutes, and then transfer to a wire rack to cool completely.