Third Earth is experiencing a total lunar eclipse and Mumm-Ra uses this eclipse to cast a spell that will cause Cats Lair and everything in it to malfunction. The Thundercats first notice this when things start falling apart and fail. Lion-O and Panthro must fight the Mutants while having problems running the Thundertank. They still manage to defeat the Mutants, but crash the Thundertank. Lion-O realizes that this must be Mumm-Ra's evil work and goes to the pyramid to stop Mumm-Ra. Meanwhile Cats Lair is getting worse as Cheetara and Tygra rush to fix things in the lair but are attacked by the Lunataks. They defeat the Lunataks temporarily, but the Lunataks return to finish off the Lair. In order to break the spell, Lion-O must use the Sword to block out the sun (thetvdb.com)