Time for a new book, and this one will only be in two parts, I think! It's He-Man and the Masters of the Universe in "The Sword of Skeletor"!
In case you don't want to do the clicky thing to get a larger view, I'll provide a running summary. He-Man's leading the Masters to Point Dread, where Skeletor's demons are attacking!
The battle is won, but suddenly a watery hand pulls He-Man under, where Mer-Man steals the Power Sword!
He-Man escapes from the tangleweeds that had held him, and Mer-Man delivers the sword to Skeletor.
Joining He-Man's sword to his own, Skeletor uses the reunited sword to open Castle Grayskull!
Yikes! Not sure what happened with my scan here! Anyway,the Masters reach Greyskull, but feel there's no hope... but someone else says it's never hopeless!
And I just now realized that my copy of this book is missing the centerspread, so I can only assume that the Sorceress appears to give He-Man hope, and to show him a secret way into the castle... and we'll see what happens after that next time!