The character Frank Irving's last name is an homage to Washington Irving, the author of the original story of Sleepy Hollow.
Most of the spells are spoken in Greek (though not with a very good translation).
The Headless Horseman is depicted as wearing the traditional "redcoat" uniform of the British Army. However, the Hessian mercenaries employed by Great Britain wore their own distinct uniforms. The most common were a green coat with red trim, or a blue jacket with gold trim.
In the opening sequence, in the clip after the horse with a red eye, you can see Ichabod and his wife walk slowly toward each other. In the middle of them, you can briefly see a shadow of the demon Moloch dancing.
One of the spells is in a Ghanaian local dialect known as the "Twi" language.