5x19 - Hercules: The Legendary Journeys

Merlin hurled the vicious warlord Arthur of Camelot and his sorceress advisor Mab a thousand years back in time to Hercules' world. But Mab helped Arthur conquer Britannia. Later she wanted to go back to her own time, and to do that she needed to kill young Merlin with the sword of Excaliber. Hercules and Morrigan captured Arthur and the sword, but mab took Merlin hostage. A fierce battle ensued, during which Hercules dispatched a giant knight and a reformed Arthur displayed newfound heroism. Merlin smote Mab, and Arthur returned to his own time as a proponent of peace.