Wikipedia has it that 'The Mari Lwyd (Grey Mare or "Gray Mary" in English), also Y Fari Lwyd, is a Welsh midwinter tradition, possibly to celebrate New Year, although it formerly took place over a period stretching from Christmas to late January.

It is a form of visiting wassail, a luck-bringing ritual in which a the participants accompany a person disguised as a horse from house to house (including pubs) and sing at each door in the hope of gaining admittance and being rewarded with food and drink.'

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