Mari Lwyd, the grey mare, a horse skull on a pole, taken round with singing at New Year. There's also the Crwmpyn John play from the Swansea Valley, an English type mumming play. This was performed, in English, in communities that spoke Welsh. In some cases, the words to Crwmpyn John were the only English known.

Gower also had a traditional mummers play of the English type, as did many other areas of South Wales. There has been so much movement back and forth over the Severn river in the past thousand years that it's pointless trying to establish a firm border for folk culture.

I've not heard of Souling in South Wales (the above are Christmas/ New Year customs) but North Eastern Wales has close cultural links with Cheshire, and I wouldn't be surprised if Souling took place there sometimes.