Add the mint and a bunch of the red berries into the cocktail shaker and muddle them together. Add the gin, the Vermouth, the red berries juice and the ice and shake vigorously. Strain the liquid into a cocktail glass and top up with soda water. Add a few whole berries and some mint in the glass, for decoration.
Now the fun part: Rudolf! Push the two cloves into the marshmallow to create the eyes, and the two rosemary springs on top, to create the antlers. Then make a small hole with a knife in the middle and insert a cranberry, for the red nose. Add Rudolf on top of the glass, to impress your friends.