The Mari Lwyd (the Grey Mare) is a pre-Christian tradition said to bring good luck.
People made a horse figure from a horse’s skull, with decorative ears and eyes attached. They adorned it with colourful reins, bells, and ribbons and wrapped it with a white sheet that is carried around on a pole.
The Mari Lwyd and its party would go door-to-door, singing and challenging the families inside to a battle of rhyming insults in Welsh. At the end of the battle of wits (known as pwnco) the group would be invited into the house for refreshments.
This old tradition died out in many parts of Wales, but some parts still act it out and every December you can see it at the St Fagans: National History Museum. Each January several Maris from different regions gathers in Chepstow for the Chepstow Wassail Lwyd.
For lots more images of Mari Lwyd, check out the Mari Lwyd Flickr group.