The hunt begins with the conditions imposed by Ysbaddaden upon Culhwch, who wishes to marry the giant's daughter Olwen. The required grooming tools lie between the ears of Twrch Trwyth, a former king transformed into a boar. Arthur brings a great company to Ireland, where the quarry is accompanied by seven young pigs. Their refusal to surrender is voiced by Grugyn Silver Bristle. Llwydawg has no separate dialogue in that encounter, but he belongs to the family that then crosses the sea and brings the struggle into Arthur's country.

At Dyffryn Llychwr, Grugyn and Llwydawg turn against the hunters together. The narrative says that they kill all but one of the men who close upon them. Arthur arrives with further men and hounds, and the noise brings Twrch Trwyth back to support the two young boars. This is not a separate campaign by an unrelated monster. Llwydawg's resistance is part of the family's defence during a pursuit in which hunters, hounds and quarry repeatedly change direction and regroup.

The losses accumulate around Mynydd Amanw and Dyffryn Amanw. An unnamed pig is killed, followed by Twrch Llawin, Gwys, Banw and Benwig in the sequence of the chase. Only Grugyn and Llwydawg remain with their father after this stage. At Llwch Ewin the larger boar makes another destructive stand, and the route then reaches Llwch Tawe. Grugyn separates from the others and heads towards Din Tywi and Ceredigion. The tale follows these movements through a dense chain of place-names rather than giving either young boar a complete independent biography.

English versions differ in the wording around Garth Grugyn. Charlotte Guest's translation names Llwydawg in the fighting there and credits him with killing Rhudvyw Rhys. Another English translation assigns that encounter, the differently spelled Rhuddfwy Rhys and the death at Garth Grugyn to Grugyn. This difference should not be hidden by awarding exactly the same last stand to both brothers without explanation. What follows for Llwydawg is clearer: he goes to Ystrad Yw, where men of Llydaw, rendered Armorica or Brittany, meet him. Their origin does not move the battle across the sea.

At Ystrad Yw, Llwydawg kills their ruler Hir Peisawg, also rendered Hirpeissawg, and Llygadrudd Emys and Gwrfoddw, called Gwrbothu in Guest's translation. Both latter men are identified as Arthur's maternal uncles. Llwydawg is then killed, bringing his own part in the pursuit to an end. Twrch Trwyth continues towards the Severn, where the razor and shears are taken, and then reaches Cornwall before the comb is won and he is driven into the sea. The father's unknown fate is different from the young boar's recorded death. Llwydawg remains a mythological animal of the Welsh quest, remembered through the companions he outlasts and the hunters who fall before him.