Inside the Black Pyramid, Mumm-Ra's cauldron is showing him a vision of Mongor, a creature who grows stronger by feeding on fear. The image shows the goat demon creating raging fires with his Scythe. Mumm-Ra, who has been searching for Mongor's prison for centuries albeit unsuccessfully, is certain that once released, Mongor will succeed in defeating the ThunderCats.At Cats Lair, Tygra and Cheetara are puzzled by sudden mysterious earthquakes and a strange force field which blocks their scanners. Out in the ThunderTank, Lion-O, Panthro and Snarf are experiencing the same technical problems with their equipment. They head back to the lair by which time the disturbances had stopped. Panthro declares everything to be normal but Tygra points out that each time the phenomenon occurs, it gets stronger.At that point, Wilykit and Wilykat admit that they are somehow responsible for all these strange disturbances. They go on to explain that earlier that day, they came across an ancient ruined temple and decided to explore it further. Inside, they found a hexagonal stone slab with strange symbols carved on it. Thinking that there might be a tomb hidden underneath it, they prised the slab and ended up releasing a fearsome goat-like creature.The adult ThunderCats are extremely annoyed at the ThunderKittens and start berating them for their irresposible and reckless behaviour. Snarf intervenes and tries to explain that the ThunderKittens are only kids and yelling at them isn't the right way to handle the situation. As all the adult ThunderCats are listening to Snarf, Wilykit and Wilykat sneak out of the lair in their spaceboards. Noticing that they are gone and concerned for their safety, the ThunderCats decide to split up and go searching for them.As Tygra is passing through a forest, he encounters Mongor. The two battle but Mongor ties Tygra up using his own Bolo whip. Next Mongor seeks out Cheetara and ensnares her in a net. Finally, Mongor cofronts Panthro and succeeds in using his own shoulder spikes to bind him and anchor him to the ground. Meanwhile, Wilykit and Wilykat return to the ruined temple and figure out that the secret to defeating Mongor is not to look at him directly.Having defeated all the other ThunderCats, Mongor seeks out Lion-O and the two engage in combat. Suddenly, Wilykit and Wilykat arrive riding their spaceboards and tell Lion-O not to look at Mongor directly. The ThunderKittens distract Mongor by blowing bubbles at him and Lion-O uses that opportunity to attack the goat demon. He turns his back to Mongor and using his Claw Shield as a mirror, fires a blast from his sword which shrinks Mongor down in size. Finally defeated, Mongor returns back to his tombs and Panthro seals it with a blow torch.