Maelgwn Gwynedd, king of Gwynedd (d.547 AD), got himself into a bit of a pickle on one occasion, by tussling with a saint - which really isn't recommended. He had entrusted his favourite white horses to St. Tydecho (King Arthur's nephew?) who was living in retirement at the northern end of the Dyfi valley at Llanymawddwy. (There's still a rock shelf named Gwely Tydecho - Tydecho's Bed - and a spring called Ffynnon Dydecho, nearby.) St. Tydecho let the horses out onto the hills, where they ate the heather and turned yellow. Be warned: never eat the jaundice-inducing heather of Mawddwy. Was Maelgwn mad! He took possession of St. Tydecho's oxen in return (but the saint wove his magic over some local stags so that they could pull his plough instead, so that was OK). And that wasn't the end of their association because, on a later occasion, Maelgwn was out hunting when he stopped to rest by a large rock, became stuck to it, and had the ignominy of having St. Tydecho setting him free.
http://www.britannia.com/bios/ebk/maelgggd.html tells these and other stories in delicious detail.Here there be Giants
I don't know if it's anything to do with the water hereabouts, but Llanymawddwy has a tradition of producing giants. One such, Llywelyn Fawr o Fawddwy, is buried in the churchyard. A local information board reports that bones twice the size of normal human remains have been unearthed, said to be of the Giant of Mawddwy (Cawr Mawddwy), who once threw a rock from the top of Aran Fawddwy, leaving the imprints of his fingers on it. This rock - Maen y Cawr - can apparently still be seen at Ffridd Wenallt, just up the valley.And Romans?
There's a report by historian Lewis Morris dated 1746 of a stone with a Roman inscription being found in a stone wall near the churchyard in Llanymawddwy which translates as "(The stone) of the daughter of Salvianus. Here (she) lies, Ve[--]maie, wife of Tigernicus. And of his daughter Rigohene. She lies (here), wife of Oneratus". Unforunately, the stone was reported lost that very same year, and has never been seen since.
A tradition which was prevalent in the area until about 1830 was called The Shot, or a financial contribution towards drinks in the local pub following a death of a villager. It was considered bad form not to take part in this, and men typically contributed a shilling and women sixpence. They were not expected to drink their money's worth, but simply to take a drink to pay their respects, and then go on their way. When the kitty ran out, the process was repeated with those who remained. The twist to this was that the names and addresses of those who contributed were recorded and the list handed over to the nearest relative of the deceased who, at the next opportunity (i.e., when one of those present, or one of their relatives, died), would return the compliment. This tradition of recording the names of benefactors brings to mind the way that, even in the 1960s, contributions to the Missionary Fund in one of Machynlleth's places of worship were published against the donors' names, in the form of a league table. Inevitably, the local Lord of the Manor and gentleman farmers were at the top, and the pensioner from the poorer part of town was at the bottom. Horrendous.
There's a tradition that Bryn Hall was haunted by a ghostly headless horseman, but the haunting ceased once the horseman was able to pass on to one of the servants the location of the buried body of an illegitimate child of the local lord.