Preying on the fragile truce between the Andreenids and the Avionians, Skeletor starts a war that threatens to tear the Mystic Mountains apart. As both tribes wage war in the skies of Eternia, Skeletor successfully obtains Ambrosia, a miracle Andreenid food that gives power to the individual who digests it. He-Man and Teela arrive to stop both the war and Skeletor...

Beast Man introduces Skeletor to the Shadowbeasts, large powerful creatures that attack at night in vast numbers. Knowing the creatures hate any light source, Skeletor and the Evil Warriors cause Mount Barathrum to explode sending out a large ominous could that blocks out the sun. Ram Man must face his fears after Teela is injured during the attack, as the heroes soon realize the Shadowbeasts are striking both the Royal Palace and Castle Grayskull!

After failing to impress Skeletor with his latest plan, Tri-Klops decides to overthrow Eternia himslef. It is not long before a near-indestructible army of Bone Monsters are making their way towards the Royal Palace! With the odds stacked against them, He-Man and Sy-Klone defend Eternia as Man-At-Arms latest creation, Roboto, a strategic chess-playing robot, attempts to convince Teela that he can aid them in their battle...