These little soul minions are released from the headless horseman when you hit him.
They will slow and weaken you, so be careful. They don't drop anything.

The Headless Horseman is a new miniboss that can rarely spawn in soul sand valleys.
He's filled with souls, and hitting him will release some of them. He'll sometimes drop
a soul scythe upon death. The soul scythe does 8 damage, and steals the life energy of
mobs to heal you.

The pumpkin spirit can spawn anywhere except for the end. It's tanky, and
very knockback resistant, so be careful. Don't get close to it, or else it will
use dark magic to blind you. They drop pumpkin seeds and sometimes pie.

Ghosts are common mobs that can spawn in the overworld. They do a lot of damage,
and carry you into the air with them. They don't have any drops.