The Magnetic Mountains are a range of mountains on Mongo with mysterious properties. When ships approach, the compass swings wildly, and the dials start spinning. The mountains are also covered with a blinding green fog.
Brown Dwarfs live in the forest at the foot of the mountains.
Captain Lin-chu pilots a prison ship across the mountains; the ship crashes, and the prisoners (Flash Gordon, Dale Arden, Prince Barin, Prince Thun and Dr. Hans Zarkov) are freed. ("The Monsters of Mongo")