Video showing how to make skulls. When finished, paint with glow paint and you have inexpensive glowing skulls. If placing on a wall, you probably don't need the back of the skull and if careful, can get 2 skulls per jug.
For Halloween: Casting with packing tape. First layer sticky side UP, then Using just the legs for halloween would be fun. layers sticky side DOWN. Round tip scissors to remove, then tape back together.