In small bowls, mix some icing sugar (around 4 tbsp) with a few tsp of water. Add your colours and mix well. We went with purple, orange and green as we thought they were the most 'Halloweeny'. Put some spinkles and eyes in separate bowls . We found some fun Halloween themed ones but you could use anything you have to hand or even some mini M&Ms. Spoon the icing on to each biscuit and decorate with the sprinkles/sweets and eyes.