MASK OF EVIL

This book introduces Lady Irena, a childhood friend of Teela and Prince Adam, who has apparently come to the royal palace to visit her old friends. But Orko catches sight of Irena sharpening a dagger and suspects something is wrong. It turns out that the real Irena has been trapped in a large crystal sphere in Slime Swamp, and the visitor is actually a lizard creature sent by Skeletor to subdue everyone by magic so he can conquer the palace. The plot is uncovered by He‑Man and the Sorceress. Skeletor is defeated and Irena is rescued before she runs out of air. There's some nice jeopardy to the story.