He-Man and the Masters of the Universe (1983)

S2E45 The Problem with the Power

Skeletor deceives He-Man into believing he has unintentionally taken a life, leading a remorseful He-Man to revert to his true identity as Adam. Overwhelmed with guilt, he discards his sword into the depths of Grayskull, feeling unworthy of its strength. Seizing the opportunity, Skeletor opens a portal to the goblin realm, unleashing General Tataran's formidable army upon Eternia, threatening to overpower the planet. Will Eternia endure in the absence of its greatest champion, and can Adam uncover the truth behind Skeletor's ruse before it’s too late?