Mxyzptlk is now two siblings, who are hawking a complete set of the Encyclopedia Universal. They put Perry White in a coma when he didn't go for their sales pitch, but after Superman proved a tougher nut to crack they went big and canceled Earth's gravity.
As the Earth falls to pieces, buildings start soaring into space, and a S.T.A.R. Labs space station begins drifting into the void, Superman and the Atom make tracks to the Fortress of Solitude. Atom's brought the white dwarf star that powered his size-changing belt. Superman says it feels heavy, though the Atom says it's 100 tons. That's not much to Superman, right, let alone for a star? Was it supposed to read 100 million tons? I guess it's a star fragment, because even a neutron star probably wouldn't fit in your hands.
Anyway, the weight is no big deal because the starlight is charging Superman up, and oh come on, it's a yellow sun that does that! I mean, yes, yellow light is contained within white light, but so is red, which would cancel out any gains of the yellow! Dang it Joe Casey, have you no respect for fictional stellar physics?
The Mxys are just floating around, watching the show, playing word association games, for some reason retconning something from earlier in Casey's run to be their doing instead of the Prankster's. They're also debating if they'd like to level up to something more than an 'annoyance.' Maybe become real super-villains, which is a terrifying notion. But as the Great Wall of China disintegrates, they find themselves encased in glowing green light. Alan Scott and John Stewart are creating a breathable forcefield around the entire planet, to hold it together.
(It's odd that, even though Superman tells everyone this is being caused by magic, we don't see any magic-users trying to do anything. Unless whatever Tempest was doing riding an orca counts.)
That gives Superman time to drill his way to the Earth's core, stuff the dwarf fragment there, then alternately heat and cool it with his powers, because the expansion and contraction produces more gravity. That done, Supes zips into space, hauls the space station back before everyone freezes of suffocates. Then it's off to confront the Mxys.
He offers to take a set of the encyclopedias, though he doesn't specify how he's going to pay, which seems like not very carefully defining the terms of a contract with the Devil. Then he pokes the bull by saying he liked them better as a funny little imp. As they reset all the damage (including to Perry's brain), speaking in unison, they disappear with a promise that, 'next time, we won't hit the reset button.'
{1st longbox, 18th comic. Adventures of Superman #618, by Joe Casey (writer), Charlie Adlard (artist), Tanya and Rich Horie (colorists), Comiccraft (letterer)}
