To make a headless horseman costume, sew the neck of a black T-shirt shut, and then cut eye, nose, mouth and arm holes into the shirt. Use an axe template to cut out a cardboard axe, and paint it black. Cut a horse's head from cardboard, and tape it to a broom to make the horse. Put on the black T-shirt, brown pants and tattered white button-up shirt to complete the costume.
Add red paint to the neck of the T-shirt to make it appear bloody. Use additional props, like a map of Sleepy Hollow or a carved jack-o-lantern to give the costume personality.
Alternatively, make the costume by cutting a large box into a long piece that fits over the head and shoulders. Use spray foam on the cardboard to create a muscled look on the biceps and chest. Once the foam dries, sculpt it into an ideal shape using a knife. Create accessories like a vest, scarf or cape using a sewing machine. Cut holes into the neck of a large turtleneck for vision, and pull the neck completely over the head to appear headless. Wear a pair of glasses beneath the turtleneck to keep it from squeezing the eyes and face. Wear black pants and shoes to complete the costume.