This is one of the vast array of novelty ice cube trays from homeware company FRED. According to the description you can:
"Chill your beverages to the bone! Fill and freeze our Bone Chillers tray and you’ll create an icy array of skulls and crossbones that’ll have everyone’s timbers shivering. Drink up, me hearties!"
Okay, so they're marketing them with a pirate theme, but they'd easily fit into a Halloween/horror party. Or, just for any occasion. Cubes are boring!
To buy one, or to browse their other products, you can check out the FRED website.