Trap Jaw's mechanical arm switches sides and back again when he tells Mer-Man about the Korridite aboard the sub.
In this story and in Eternal Darkness (1983), Eternia has only one moon. But in The Shadow of Skeletor (1984), Into the Abyss (1984) and He Ain't Heavy (1985) there are more than one.
After He-Man defeats Mer-Man's monsters we see the Widgets cheering, Squinch suddenly has his spear at hand.
When Jacob and the Widgets talk on the beach, Lora says "How awful!" and presses a hand to her cheek. In the next shot, both her hands are in her lap.