Earth's champion meets the galaxy's toughest 'Cats in a special by Judd Winick, Al? Garza and Trevor Scott! While attempting to stop Mumm-Ra's mutants from retrieving another Eye of Thundera from an alternate dimension, the ThunderCats are hurled into Metropolis! Can the Man of Steel withstand a blow from the most powerful sword in the universe?
As he prepares to do so, a bald woman, Lantana Lin, appears before Mumm-Ra, telling him that he can use to orbs to secure a second Eye of Thundera in another dimension in the city of Metropolis.
Nupil, one of the beasts Mumm-Ra once used as a slave spies on the meeting and tells the ThunderCats, who decide to ride out at dawn and stop Mumm-Ra.
As the Mutants prepare to enter the dimensional gateway, the ThunderCats attack. Lion-O slams into the dimensional gateway with the Sword of Omens, but somehow the Mutants manage to get through, pulling the ThunderCats along.
On the streets of Metropolis, Lion-O appears in front of a child playing with a ThunderCat/Masters of the Universe hybrid toy figurine. The child is saying, "Thunder, thunder, thunder-" when Lion-O appears. The people react with fear towards the ThunderCats, because they cannot understand their language. The Mutants, invisible by virtue of kryptonite necklaces they wear, attempt to escape. However the ThunderCats can still see them and they attempt to give chase, the police arrive to deal with the ThunderCats.
Lion-O, seeing Superman grab Cheetara, attacks, slashing Superman in the chest. Superman falls back in pain, his suit torn in the chest, realizing that Lion-O's sword is magic-based. Superman feels like he's been hit with Kryptonite.
Meanwhile, the Mutants head for the Eye of Thundera. Vultureman grabs it, but the ThunderCats and Superman arrive to take it back. The ThunderCats take the Kryptonite amulets and Superman takes back the Eye of Thundera.
Mumm-Ra, now upset, transforms into his Ever-Living form and attacks Superman. Superman fends him off, but Mumm-Ra starts to get the upper hand. Lion-O and the ThunderCats step in and take him down, along with the Mutants. Lion-O sends them back into the gateway, which is now re-opened, and the ThundercCats follow.
Superman goes with Lois to the Fortress of Solitude and places the second Eye of Thundera safely in a display case.