Diarmuid went out early the next day again to the hill, and it was not long till he saw the three strangers coming towards him, and he asked them would they like to see any more tricks. They said they would sooner get news of the grandson of Duibhne. "I saw a man that saw him yesterday," said Diarmuid. And with that he put off his arms and his clothes, all but the shirt that was next his skin, and he struck the Crann Buidhe, the spear of Manannan, into the earth with the point upwards. And then he rose with a leap and lit on the point of the spear as light as a bird, and came down off it again without a wound on him. Then a young man of the Green Champions said: "It is a man has never seen feats that would call that a feat"; and he put off his clothing and made a leap, and if he did he came down heavily on the point of the spear, and it went through his heart, and he fell to the ground. The next day Diarmuid came again, and he brought two forked poles out of the wood and put them standing upright on the hill, and he put the sword of Angus Og, the Mor-alltach, the Big-fierce one, between the two forks on its edge. Then he raised himself lightly over it, and walked on the sword three times from the hilt to the point, and he came down and asked was there a man of them could do that feat.
"That is a foolish question," said a man of them then, "for there was never any feat done in Ireland but a man of our own would do it." And with that he rose up to walk on the sword; but it is what happened, he came down heavily on it the way he was cut in two halves.
The rest of the champions bade him take away his sword then, before any more of their people would fall by it; and they asked him had he any word of the grandson of Duibhne. "I saw a man that saw him to-day," said Diarmuid, "and I will go ask news of him to-night."

Part II Book VII: The Green Champions
Gods and Fighting Men [1904]
Lady Augusta Gregory
Celtic Folklore
Internet Sacred Text Archive
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The wikipedia entry on The Green Knight has been parasitized by religious lunatics, and in an effort to wash the foul taste of that nonsense out of my head, turning to the Green Man entry, and from thence to Lady Gregory's scholarly valor, happily for me.