To unlock the new characters, you need the shield. Don't pay too much mind to the skeleton as it's the background that's needed. Use the background on different girls with the carved pumpkin on their head.
**Spoilers for who unlocks what**:
Enderwoman = Mal0
Sheep = Cult of Lamb (I'm unfamiliar with this character)
Pumpkin should be obvious
Bee = Hornet
**Spoilers**