The Thundercats depart Third Earth for New Thundera, leaving Tygra and Pumyra behind to watch over the Cat's Lair and Tower of Omens. Meanwhile, the Ancient Spirits of Evil resurrect Mumm-ra, building a new pyramid on New Thundera.

More and more earthquakes are occurring on New Thundera thanks to Mumm-Ra's sabotage of an arcane machine that lies at the center of the planet that holds its gravity together, watched over by the ancient Thunderian sorceress, Jagara.

Mumm-Ra sends Ma-Mutt disguised as Mandora to free the Mutants from the Circus Train. The Mutants are then ordered to get rid of Tygra and Pumyra back on Third Earth.

Mumm-Ra sends Ma-Mutt, disguised as Mandora, to free the Mutants from the Circus Train. He then sends them to Third-Earth to eliminate Tygra and Pumyra.

Mumm-Ra again seriously threatens to destroy the Gyroscope and thereby the newly reformed New Thundera. Jaga helps Lion-O think of a solution once and for all.

The Ancient Spirits of Evil bring a creature to Mumm-Ra called a Mirror Wraith, which he transforms as a doll and gives to a lost thunderian child named Leah, who keeps it and unwittingly puts the Thundercats in great danger.

Wilykit and Wilykat accidentally release Frogman. Seemingly harmless at first, he is soon revealed as a ruthless villain with the fearsome power to control all water.

While exploring New Thundera, Wilykit and Wilykat stumble upon a mysterious orb of gold and pick it up, believing it to be one of the Treasures of Thundera. However, it soon transpires that that is not the case.

Jagara cannot work the new Gyroscope alone, so the Thundercats send for someone to aid her. Screwloose, a robot who specializes in the technology, comes to Third Earth. But, Mumm-Ra tampers with his programming, making him destructive.

Mumm-Ra resurrects the ancient alchemist Malcar, but he returns old and weak. Mumm-Ra then sends him to the Canyons of Youth, which will restore his youth and power so that he may effectively defeat the Thundercats.

Panthro, Snarf, and later even Mumm-Ra fall prey to the waters of the Swamp of the Laughing Lillypads-which unless cured, will cause them to laugh until they die.

The twisted robo-pirate Captain Cracker frees the Lunataks from the Circus Train and they all plot to assault Third Earth, since most of the Thundercats are on New Thundera.

While on a solo trip to New Thndera, Tygra crash lands in an unexplored region of the planet's moss-land. There he is captured by a mysterious and mighty gigantic swamp beast.

Mumm-Ra has a powerful device called the Babylonian Babarian Boiler, that he plans to use against the Thundercats. However, the bumbling Ma-Mutt accidentally destroys the machine, causing an enraged Mumm-Ra to banish him from the pyramid.

The Ancient Spirits of Evil unleash the Shadowmaster, a dark sorcerer who may be even more powerful than Mumm-Ra. Fearing the Sprits will favour the Shadowmaster over him, Mumm-Ra hatches a secret plot to aid his enemies the Thundercats.

An ecology inspector comes to New Thundera to inspect the new Cat's Lair. His ship uses the Space Way Airborn Navigation system to direct him to planets throughout the universe. Upon arriving he is ambushed by Two-Time, who steals the ship. Written by adamlee

Mumm-Ra reluctantly summons up the treacherous tentacled demon Amortus, who has the formidable ability to turn all living things into stone.

Vultureman escapes the Circus Train by hijacking a bookmobile. He discovers information about a powerful enemy of Mumm-Ra, Zaxx. Using this knowledge, Vultureman plots to overthrow Mumm-Ra and rule the universe.

Lion-O unwittingly drinks tainted water from the devastating Well of Doubt, which causes him to lose all his courage and self belief.

The key to the Book of Omens is finally solved and it is unlocked. All of the team must pass different tests to save the planet, and Lion-O faces many trials within the book to prove himself once and for all as Lord of the Thundercats.