Basically the same scenario we saw in Uncanny Avengers, but flipped to DC:
Exitar believes someone on DC earth was responsible for slaying one of his kinfolk, and decides DC earth must be destroyed.
-This is post-Flashpoint DC.
-Only earth-based characters can participate.
-The earth has 48 hours of prep, and all the knowledge pertaining to Celestials that Marvel earth had.
Can DC earth come up with a solution to stop Exitar, or is the earth's fate unavoidable?
With 48 hours prep they can probably manage something, maybe Spectre backed by the JLD can manage some magic shit like they did against that evil entity they fought a few years ago.
Overall though, it's pretty tough to stop a guy from destroying your planet when all he has to do is step on it.
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Besieged by countless foes, his eyes they are aglow, longing for the fight. He stands upon a mound, doesn't aim the throw, just lets the hammer fly!
The only hope I see is Flash. He has to really IMP (galaxy level at least) and do all the crazy shit that he can (steal speed, vibrate through, time travel to get it right, etc). Does anyone know how to create hyperspace energy in D.C.? That might help. Maybe blackholes will help too. Superman sundipping will definitely help. Have Supergirl and Superman sundipped, Flash do galaxy level IMPs, steal speed, go back in time (if he messes up), etc.