The Horde resurrect Monstroid from the bottom of the Sea of Rakash, with the help of Modulok's newest invention, Multi-Bot. Apparently, Monstroid was one of the legion of monsters banished eons ago by the Ancients.
The Horde show up to meet Monstroid, but so does Skeletor -- to control him as a tool of destruction. He-Man and gang are alerted of the problem and head down as well. Extendar is temporarily imprisoned by Mulit-Bot, while Skeletor, unable to control the monster, is attacked.
He-Man goes to save Skeletor, but ends up being captured as well. Monstroid begins to head off to the sea, but Extendar breaks loose and heads after them.
It turns out that Orko is able to force Multi-Bot to help Extendar, which in turn allows He-Man and Skeletor to be released (after 12 minutes underwater).
Orko then causes Multi-Bot to swim into Monstroid's mouth. Apparently Monstroid doesn't like the taste, and swims back to the depths of the sea.