In Wales, the Mari Lwyd custom uses the skull of a horse.
The Mari Lwyd is a South Welsh wassailing tradition associated with Christmas and New Year celebrations. A horse’s skull is decorated with ribbons, mounted on a pole, and covered behind with a white sheet that conceals the person carrying it. Some versions have movable jaws or glass set in the eye sockets.
Groups traditionally carried the Mari Lwyd from house to house and requested entry through improvised songs. The residents answered with their own verses, creating a playful contest of rhyming insults and wordplay before allowing the procession inside. The custom was first recorded in 1800, although its origins may be older.
The answer is specifically horse, not ox, deer, or goat. Historical substitutes sometimes included wooden or paper horse heads, but the skull-based form that defines the custom is equine.