If there was one thing Merlin hated more than hunting, it was hunting during winter.
"Sire, I am sorry to say that I doubt there's still anything alive this time of year." One of the two accompanying knights spoke
"I'm not going back empty handed." Arthur said decisively.
Merlin shrugged when the knight gave him a meaningful look. He's the king, what do you want me to do about it? Arthur was persistent, he wanted to catch something even if it were nothing more than a rabbit.
Another hour passed and Merlin and the knights were freezing their buts off when Arthur finally called off the hunt. He, Arthur, was grumpy because he always returned with something and now his pride was hurt which did not bode well for Merlin's chores.
On their way back that they heard rustling in the bushes and Arthur got cocky. As he tried to find out what it was he got pushed off his horse and whatever it was also took down the accompanying knights. Merlin recognized the beast as a cockatrice, Arthur had told him about it after saving him from certain death. The beast had his eye on him, Merlin, who saw best to grab one of the fallen knights' shields. Merlin was launched from his feet by the incredible charge of the beast before he could brace himself. Although he did block the blow he felt an incredible pain as he rolled down the road towards a frozen lake. The cockatrice had already lost it's interest in Merlin and was going after Arthur who was stumbling to get back on his feet. Arthur followed Merlin's path to the lake while trying to protect both Merlin and himself from the beast's assault.
"You alright?" Arthur asked between the near rhytmic bashing. "My arm." He replied.
Arthur saw Merlin's left arm just hanging by his side, probably broken, and had already brought the shield to his right.
Looking at the damage Arthur had unintentionally dropped his guard to the point that the beast's vigor forced him to his back, knocked out. Following the heavy blow it turned it's attention to Merlin once more. Merlin wasn't a fighter and not that heavy, the cockatrice bashed him onto the icy surface of the lake. Thankfully he was more prepared than before and the assault would only leave some minor bruises. An idea came to his mind and began to shout at the creature before it could shift it's attention back to Arthur once more.
"Over here you filthy lizard." Merlin began crawling back as the vilainous reptile joined him on the slippery surface. It seemed reluctant to go after him but bravely pressed on further onto the lake. Every time Merlin heard a crack he feared for his life, he wouldn't last long in this water but neither would the cockatrice, which he was hoping for. Then another crack and the beast fell into the water to it's demise. It tried to climb back onto the ice, breaking bits and pieces as it did, but it proved too slippery.

Silence

Merlin let out a sigh of relief. This had definitly been one of Arthur's worst moments of bravery. He stood up, forgetting how thin the ice was, and the ice cracked, plunging him into the water. Noticing that the shield he was still wearing didn't float, it was the first thing he allowed it to depart to the cold depths of the lake.
Merlin tried to pull himself up and back onto the ice but with a broken arm it wasn't very easy. He felt like the cockatrice and he would end like it. Then his fingers managed to get some grip on the ice and he was able to keep himself steady. The cold had numbed the pain in his arm, allowing him to use his other hand even if only to steady himself further. Despite his arm's temporary recovery he lacked far too much strength to pull himself up. All he could do was hang there until someone would come to his rescue.
"Help!" He shouted. "Help!" He screamed in an unusually pitched voice. He kept calling for help but his cries went unheard and, much to his despair, it seemed that the colder he got, the softer his voice had become became. By the time he decided to call Kilgharrah his voice had become too soft for even the birds to be heard. He was losing the battle with the cold, his lips seemed to stop moving although he lost sense of them long ago. His sight began to blur and darken as he lost his grip until he finally let go, allowing the darkness to consume him but with the comfort that he would be embraced by Freya's arms, even in death.

AN:
No, he's not dead yet. Wouldn't be much of a Mergana story if it were, would it?