An Ecology Inspector (EI) comes to Thundera to inspect the new Cats Lair. His ship uses the SWAN system (Space Way Airborn Navigations) to direct him to planets all over the universe. When he arrives on Thundera, he gets ambushed by Two-Time (see Return to Thundera, Part III). Two-Time uses a hologram to make the EI's ship crash into a mountain, and then when the Thundercats come to rescue the EI in the Feliner, Two-Time uses the hologram again. Lion-O manages to fly around the mountain and lands the Feliner. Meanwhile, Two-Time flies to new Cats Lair in his spaceship, Dome-Down. He actually picks up the whole Lair and keeps it inside Dome-Down. The Thundercats fix the Feliner, rescue the EI, and then fly to catch Dome-Down. Once they catch the spaceship, Lion-O uses the sword to defeat Two-Time and send him flying out of the ship. Then they return Cats Lair to its proper place.

The episode was rated 7.63 from 19 votes.

Tygra, on a solo trip to New Thundera to meet the other Thundercats, decides to take a shortcut through a meteor shower. His ship is damaged, and he lands on an unexplored region of New Thundera. The Moss-Land. It turns out that the moss in moss-land is part of a giant monster who captures Tygra with its moss. Lion-O and Panthro set out to save Tygra and battle the Moss Monster.

The episode was rated 7.81 from 16 votes.

Jaguara cannot work New Thundera’s Gyro on her own. The Thundercats order a robot to aid her in running the Gyro. Screw Loose, a robot who specializes in Gyro’s, comes to New Thundera. Mumm-Ra manages to mess up Screw Looses brain so he becomes destructive instead of helpful. The Thundercats must help Jagara get Screw Loose under control, before the entire planet is destroyed.

The episode was rated 7.81 from 16 votes.

Mumm-Ra summons Malcar, an ancient alchemist, to return from the dead. The alchemist returns old and weak, as he was when he died. Mumm-Ra takes him to the forest of youth to restore his youth and power. Malcar regains his powers, and uses them against the Thundercats. He transforms all the Thunderillium on the planet into Thundrainium.

The episode was rated 7.83 from 18 votes.

From the Shadow Realm, the Shadowmaster contacts the Ancient Spirits of Evil (ASOE), telling them of how he captured Lion-O's father, Claudus, just before Thundera blew up. Then the Shadowmaster, through a bad dream, shows Lion-O his captured father and challenges Lion-O to a fight. Lion-O goes to the Shadow Realm through the Book and Sword of Omens, and is able to fight the Shadowmaster as long as the Sword stays bonded to the book. However, the Shadowmaster sends a huge bat to steal the Sword. It succeeds, and then Lion-O becomes very weak in the Shadow Realm. Mumm-Ra meanwhile, feeling like the ASOE will turn against him in favor of the Shadowmaster, sends Ma-Mutt to secretly steal the sword from the bat and put it back near the book. This renews Lion-O's strength, who calls for the Sword, rescues Claudus, and exiles the Shadowmaster. Claudus leaves Lion-O, but at the end you see him and Jaga standing next to each other in that blue, ghostly form. Now Lion-O has 2 mentors to give hi

The episode was rated 7.84 from 19 votes.

Capt. Cracker and his mechanical parrot Polly land on Way-Out Back and free the Lunatacs and put Bragg and Crownan in one of the train's cages. They plan to go to Third Earth to attack it since most of the Thundercats are no longer on Third Earth. Meanwhile the ThunderCats have learned Cracker escaped and Snarfer and Mandora go to catch him. Bragg has Crownan ride a fire exstiquisher, so he can get into space and get help. Mandora finds him, and the three of them go to Third Earth. Mandora fights with Cracker and the Lunatacs, but is beaten and she and Snarfer are tied to her cycle and sent towards a mountain. Lion-O, Panthro, and Cheetara arrive and Lion-O saves Mandora and the others. Meanwhile Cracker and the Lunatacs go to attack Cats Lair, only occupied by Pumyra, but Lion-O uses the Eye's signal to cause the drawbridge to tilt, sending Cracker and the Lunatacs into the moat. The Lunatacs are exiled again.

The episode was rated 7.88 from 17 votes.

A convergence of the Moons of Plun-Darr causes a drought on Thundera. Panthro and Snarf go looking for water, then Ezuka, the flying Serpent of Dreary Canal wanting to get water itself, attacks Panthro and Snarf and causes them to fall into the Swamp of the Laughing Lilypads, making them laugh out of control. Ezuka attacks the Lair, still looking for water. Lion-O uses the Sword to make some rain, then he and Ben-Gali use the Thunderstrike to melt some ice, but Mumm-Ra comes along and causes a flood. Lion-O calls for the others, which also free Panthro and Snarf from the laughter and they use some of the Swamps water to cause Mumm-Ra to laugh uncontrolably, and he falls in the flood waters and is washed away.

The episode was rated 7.93 from 14 votes.

Wily Kit and Kat are constructing a well for the New Cat's Lair on New Thundera. The Thundercats on New Thundera receive a distress signal from Thunderian refugees trying to find their way to New Thundera. The Kittens are left alone with Snarf on at the New Cat's Lair, and Lion-O and Snarfer are out constructing an early warning device (I guess for weather purposes). The rest of the Thundercats seek out the refugees in space. When Wily Kit and Kat strike water, they accidentally unleash a monster that Jaga trapped in the underground lake centuries ago. Frogman, with aquatic powers, tries to sink the New Cats Lair. Lion-O however re-traps Frogman in his watery prison.

The episode was rated 7.94 from 18 votes.

The Ancient Spirits of Evil bring the Mirror Wraith to Mumm-Ra, and he disguises it as a child's toy. Mumm-Ra then intercepts a thunderian escape pod which carries in it a little girl. He gives the toy to the child (Leah), and leaves. She is rescued by the Thundercats, and goes into New Cat's Lair with the doll. The doll turns into the Mirror Wraith when left alone, and begins to destroy Cat's Lair, and the Thundercats have no clue where the evil Mirror Wraith came from.

The episode was rated 8.11 from 19 votes.

New Thundera is being torn apart and the Thundercats must present certain artifacts at various dangerous locations that used to be beautiful places, then Lion-O must go into the book and give the Key of Thundera to the guardian of the book ""at the 24th hour,"" or the Thundercats will be frozen in time and New Thundera will be destroyed. But Mumm-Ra steals the book and key and journeys into the book himself. He wants to save New Thundera BUT wants the Thundercats frozen in time. The Ancient Spirits of Evil try to stop Mumm-Ra because they fear if Mumm-Ra goes into the book, their powers will cease to exist. The other Thundercats run into problems also at the locations they are supposed to be at. Lion-O goes into the book using the Sword of Omens and battles Mumm-Ra one on one, neither of them using any magic. Even when Mumm-Ra cheats, Lion-O still wins. The ASOE summon their ""champion,"" Pyron, to then fight Lion-O, but Lion-O gets the dragons in the book to fry him... He presents the key

The episode was rated 8.14 from 28 votes.

Mumm-Ra sends Ma-Mutt disguised as Mandora to free the Mutants from Capt. Bragg's circus train and sends Bragg and Crowman falling into deep space. The Mutants are then ordered by Mumm-Ra to get rid of Tygra and Pumyra. The Mutants attack Snowman on Hook Mt. and Snowmeyow gets Pumyra for help and Tygra contacts the real Mandora to save Bragg and Crowman. Then together, they recapture the Mutants. Meanwhile on New Thundera, the earthquake tremors grow worse and the new Cats Lair collapses trapping Snarf in the ruins. Lion-O uses the sword to contact the other Thundercats and they rush to the Lair to save Snarf. Afterwards, Mumm-Ra destroys the Gyroscope's regulator...

The episode was rated 8.15 from 20 votes.

Mumm-Ra orders Amortus, a being he banished to the Land of No Return centuries ago, to destroy Lynx-O. Amortus makes Lynx-O crash in the Thunderstrike, and then he touches Lynx-O's face. The spell from the touch makes Lynx-O feel like he is an outcast, so he leaves to join Amortus in the Land of No Return. The other TCats, Lion-O, Panthro, and Cheetara, go after him. In the Land of No Return, Amortus again touches Lynx-O, this time causing him to turn to stone. The other TCats arrive and try to beat Amortus, but he touches all of them, causing them to start turning to stone. But just as Lion-O is about to turn entirely to stone, he calls the Sword and it breaks them free. It also releases other warriors trapped by Amortus, and they all come and defeat him. Lynx-O is rescued just in time- just before the stone is permanent- and they all go home

The episode was rated 8.17 from 18 votes.

After another earthquake caused by Mumm-Ra ruins the new Cats Lair construction site, the Thundercats go to see Jaguara and confront Mumm-Ra. Unfortunately, Mumm-Ra puts up a force field over entrance. Jaga appears to Lion-O and tells him to use the Eye of Thundera to get to Jaguara and the Gyroscope. Lion-O does so and battles Mumm-Ra, who throws him into the bottomless pit underneath the Gyroscope. Lion-O however, manages to throw his grappling hook to the top, which pulls him back up. Lion-O then shines the signal, which goes through the force field. All the Thundercats leap through the signal which takes them through the force field. Together, they fire all their weapons at Mumm-Ra and he is defeated. But before he leaves, he breaks the cord that holds the Gyroscope above the pit and it falls through. Now, New Thundera is literally falling apart. But Lion-O throws the sword in the spot where the Gyroscope used to be and calls upon the Thundercat Ancestors for help. The sword starts

The episode was rated 8.19 from 21 votes.

The Thundercats use a new Tower signal to guide a Thunderian ship in; aboard are Baron Tass and Mr. Grubber, a devious pair of Thunderians. Later Lion-O sends Torr, Baron Tass and Mr. Grubber to get water, but on the way the Baron stops at the Well of Doubt and gets some of its water. The water causes a person to become very doubtful of his own abilities. When they get back to the Thundercats, Baron Tass gives some of the water to Lion-O. On the way to inspecting the new Tower in the Whisker, Lion-O feels the effects of the water and causes the Whisker to crash. Tass comes back (from getting his Guardsman, giant stone-men), and has them attack the Thundercats. Jagara has the others hold the Sword, and when Lion-O grabs hold of the sword, he's free of the water's effect. Then he fights off the Guardsman, and makes a storm, which causes the Guardsman to fall apart, and Tass promises to change his ways.

The episode was rated 8.21 from 14 votes.

Vultureman escapes from exile by hijacking a bookmobile. He finds a disk containing ancient history about two powerful evil forces on Third Earth: Mumm-Ra and his enemy Zaxx. Zaxx used a Rosencrest medallion, but Zaxx was defeated when Mumm-Ra stole the medalion trapping Zaxx in it. Vultureman plots to get the medalion, defeat Mumm-Ra, and rule the universe. So Zaxx uses Vultureman to find and defeat Mumm-Ra. But there's a terrible ""side effect"" to the medalion, anyone who wears it loses his own life and BECOMES Zaxx. When Vultureman learns of this, he changes his mind. The Thundercats get caught in this situation when Vultureman attacks Panthro and Snarf and after they crash, Snarf dissappears. Zaxx then uses Snarf to attack Mumm-Ra and Zaxx takes over Snarf's body. The other Thundercats arrive and save Snarf. Mumm-Ra defeats Zaxx once more by takin the medalion, but the pyramid also collapses on Mumm-Ra.

The episode was rated 8.25 from 20 votes.