The Zaxx Factor (S04E18)

Vultureman breaks free from his exile by taking control of a bookmobile. He discovers a disk that reveals ancient tales of two formidable evils on Third Earth: Mumm-Ra and his rival, Zaxx. Zaxx had wielded a Rosencrest medallion but was ultimately vanquished when Mumm-Ra seized it, trapping Zaxx within. Vultureman hatches a plan to acquire the medallion, eliminate Mumm-Ra, and conquer the universe. However, Zaxx manipulates Vultureman to assist in his quest against Mumm-Ra. Unbeknownst to Vultureman, wearing the medallion leads to one's demise and transformation into Zaxx. Upon learning this, Vultureman reconsiders. The Thundercats get embroiled when Vultureman ambushes Panthro and Snarf, causing a crash that results in Snarf's disappearance. Zaxx then uses Snarf to attack Mumm-Ra,