Headless Horseman

He is not a world enemy and nothing summons him directly. He only appears during the Pumpkin Moon, which you start yourself with a Pumpkin Moon Medallion at night, and he does not enter the rotation until the event is already several waves deep. That puts him behind Plantera twice over: the medallion needs post Plantera dungeon material, and reaching his wave at all takes enough killing power to push the event that far.

Once he starts spawning he keeps coming for the rest of the night. He is worth a large chunk of wave progress each time he dies, so he is part of how you climb toward Pumpking rather than only an obstacle in the way of it.

He runs on the same logic as a unicorn: long ground charges broken up by short quick hops that clear terrain without costing him speed. Nothing you hit him with interrupts that, since knockback does not touch him. If you want to learn the timing before the moon rises, a Unicorn Statue reproduces the movement in a controlled space for free.

What he adds on top is a thrown pumpkin head that weaves toward you and keeps tracking for a long time. That is the attack that punishes the obvious answer of getting high and staying still. Height stops the charges, not the projectile, so you still have to keep moving.

• He is tall. A gap of four tiles or less is closed to him completely, which is the cheapest counter available.
• Melee is where he is worst for you, because his contact damage is heavy and you cannot push him away from you. Weapons that apply damage continuously still slow his approach even without knockback.
• A long platform well above the floor keeps the charges off you, but build it too long and the event happily spawns other things onto it next to you.
• Open flight room beats clever terrain. Most of the Pumpkin Moon roster is solved by having somewhere to go.

The Horseman's Blade carries his name and does not drop from him. It comes off the Pumpking instead. His pumpkin heads travel in the same lazy S curve as the Medusa Heads from Castlevania, and the character predates Sleepy Hollow by centuries in European folklore, though that story is what made him famous.