Super Superman vs OA
Ok, Surfer leads Galactus to DC earth. All the DC superheroes/villains bands together and manage to utterly destroy the surfer but they were too late (lets assume it took too long for them to stop bickering with each other on what exactly to do. Let's also assume that the Spectre is nowhere to be found...) as he's already led Galactus to DC earth. In a massive battle, Galactus manages to subjugate the assembled heroes and prepares to munch on the planet. In a fit of Supreme heroism, Superman offers himself to Galactus as his herald if Galactus spares earth. Galactus agrees.
He empowers Superman with the Power Cosmic and wipes out his mind just as he did the Surfer and they fly off to seek other worlds.
Decades later... Superman comes accross OA and decides that this world is perfect food for his master. The Guardians figure that if they can destroy cosmic-powered Supes before he can inform Galactus, they stand a chance of stopping their planet from being eaten. They figure that they prevent him from leaving OA and then destroy him before Galactus arrives. They figure they have less than an hour to do so. They summon all the Gls who can arrive on time and brace themselves for the battle ahead.
Can they dooo eeet?