You decide to try on the reindeer harness first, and see what it was about as you place it around your neck. To be wearing something a reindeer usually wore was something a bit silly to see happen. That was, until you began to feel tingly in your body, when your feet were getting weird. You decide to see what was happening.
First you took off your shoes, and socks, and discover that your feet were extending, while your toes began to harden, while fusing with the nails they had attached to them, as they became black cervine hooves. You could also see dirt brown fur grow on your feet, on top of the hooves your toes have become, as they crawled onto your legs, causing your knees, and thighs to change as well. This forced you to take off your pants, and underwear, until you begin to watch your genitals change next.