Amortus is a strange being who was once banished to the Land of No Return by Mumm-Ra.
The Touch of Amortus involves marking his victim on the cheek with his tentacle, thereby making it possible for him to communicate telepathically and place suggestions in the victim's mind. The Touch can also turn said victim to stone.
Long ago the mighty Mumm-Ra fought and banished the creature known as Amortus, to The Land of No Return centuries ago.
In an effort to destroy the Thundercat Lynx-O. Mumm-Ra lifted the banishment. Amortus's spell makes Lynx-O feel like he is a danger o the others, so he leaves to try and protect them in the Land of No Return. Lion-O, Panthro, and Cheetara, go after him.
In the Land of No Return, Amortus starts turning Lynx-O to stone. The others arrive and Lion-O is about to turn entirely to stone, he calls the Sword and it, along with all of Amortus's past victims defeat him.