Bat Shaped Ice. If you really want to be extra, use a bat silicone mold to make bat-shaped ice!
Toy fangs. Yes, they're plastic, so not the highest quality thing, but they're a great garnish for adults when you want to make it festive. Of course, please remove the fangs before you drink it. It's just decoration. If you want to skip the plastic fangs, go for ice cube fangs instead!