Mumm-Ra, The Ever-Living is an episode from ThunderCats Roar, which originally aired on April 11, 2020.
Official Summary[]
Every time Mumm-Ra gets ahold of a magic artifact to restore his powers, the ThunderCats just smash it and turn him into a dinky skeleton again. Until today that is, because Mumm-Ra just remembered he's got the Ancient Spirits of Evil on his side.