Melt the marshmallows and golden syrup in a pan, then stir in Rice Krispies. Working quickly, pack the mixture into ice cream cones and push a lolly stick into the middle of each one. Chill the cones for 1 hr until completely firm. Mix icing sugar with green food colouring and enough water to make a thick icing. Dip the cones into the icing and decorate with sweets and sprinkles. Prop up on a wire cooling rack to set.