ThunderCats S03E12 - Return of the ThunderCubs

Panthro, Tygra, and Cheetara return to New Thundera in the Feliner to find more of the Treasure of Thundera, but Mumm-Ra shoots the Feliner down and, as the Fog of Despair, sends them to the Canyons of Youth, which changes them back into Thundercubs. Then Mumm-Ra disguises himself as Lion-O and tells the Thundercubs to find the treasure for him. Meanwhile, back on Third Earth, Lion-O and Snarf decide to go rescue the Thundercats on New Thundera, but they must ask the Mutants to take them to New Thundera in the Rat-Star. The Mutants agree, secretly planning to attack Lion-O once they're in space. They do attack and imprison him and Snarf on the way to Thundera, but they manage to break out. Cheetara meanwhile, using her sixth sense, locates part of the treasure, the Mirror of Truth. The real Lion-O shows up, and uses the Sword of Omens with the Mirror of Truth to restore the cubs to their proper age, and Mumm-Ra reveals himself and turns into Mumm-Ra the everliving.