The Welsh Christmas house-to-house horse-skull custom is called Mari Lwyd.
Mari Lwyd is a Welsh midwinter tradition in which a decorated horse’s skull, or a model representing one, is carried from house to house by people accompanied by singers. The group traditionally asks for entry through a series of rhyming exchanges known as pwnco, or wassailing verses. Hosts may respond with their own verses before allowing the party inside.
The custom is especially associated with South Wales and is generally performed around Christmas and the New Year. The horse figure is often draped in a white sheet and decorated with ribbons, bells, and other ornaments.
Mari Lwyd is sometimes described as an ancient pre-Christian survival, but its precise origin is uncertain. Its documented history is strongest in Welsh folklore and local custom rather than in a single securely dated pagan ceremony. It is also different from a standard hobby horse, which does not necessarily use a horse skull.