The duel between Arthur Pendragon and Knight Valiant occurred when Arthur Pendragon and Sir Valiant, both participants of the Tournament of Camelot, were fighting in the last battle of the finale. Valiant had a magical shield, which he had previously used on Sir Ewan and was planning on using against Arthur as well. Since he was not able to prove to the court that Valiant's shield was magical, Merlin learned the animation spell so that he could bring the snakes to life during the battle.
Although Arthur had previously had a chance to forfeit, he denied. He met Valiant in the Tournament pitch the next morning. Their duel was fierce. During the battle, Arthur knocked off Valiant's helmet, and to make it a fair fight, removed his helmet as well, much to the delight of the crowd who was watching. Then, Valiant knocked him to the ground and stepped on his shield and disarmed him. After, Valiant viscously pinned Arthur against a wall, however, Arthur shoved Valiant off him. Now unarmed, Merlin realised Arthur was in grave danger, he cast the Animation Spell on Valiant's shield, turning the snakes to life. For a moment, Valiant didn't understand what was happening because he hadn't summoned the snakes. But soon after, he took advantage of the moment and ordered the snakes to kill Arthur. But before the snakes could harm him, Morgana threw a sword to Arthur, who caught it; killed the snakes; and ran the sword through Valiant, thus winning the tournament once more (Valiant).