Every night when it is a full moon, you become a stallion. One night during a full moon, you encountered something in the bushes, and found it was a wet stallion's penis, covered in cum. You try to find the rest of the horse, but instead it just shoved its rod down your throat, causing you to swallow all of the cum it was covered in.
The stallion that throat raped you galloped off once he was done, and you were left with a contagious full moon curse that couldn't be reversed, and couldn't be wear off until the full moon night was over. Your horse form has a mane the same color as your own hair, a matching long tail, white fur, and a large pink penis long enough to penetrate a regular horse. All you know is, once the full moon comes around, you will be in for a time that will make you hung like a horse.