Coflein is giving nothing away about this stone. But there is a story that relates to its vicinity:
A tradition connected with [the slopes above the stone], and related to me by the present tenant of Waen-canol, runs thus, and must be taken for what it is worth: “A great battle was fought on this spot by two armies of Welshmen, commanded by two brothers. The fight had been in progress some time, and the slaughter had been great, when the two brothers met in mortal conflict, while the other combatants ceased fighting to watch the struggle. A terrible thunderstorm, however, sprang up, and so fearful were the flashes of lightning that they thought it was a sign from the heavens to make peace, and they did so.”
From ‘Archaeological Notes and Queries’ by A Stepney-Gulston, in Archaeologia Cambrensis 15:60, 1898.