DC X Marvel: Super Teen Battle World
The world was once one of marvelous towers of achievement. Superman, Batman, Captain America, Ironman... they were the things of legend. Their names known to every man and woman in the world. And slowly over time more and more supers began appearing-- whether it be a fluke of genetic mutation, a freak accident with radiation, an alien that crash-landed on earth, someone who was blessed with the ancient mystical powers of a god, or a scientist who had created some new advanced technological device.
Many of them set themselves to doing good. So many more used their new found powers to selfish or destructive ends. And as the years went on, these superheroes and supervillains began to train others to follow in their footsteps, often starting them off as quite young child soldiers they would call "sidekicks" or even those who aspired to be like their idols without receiving much guidance.
But then one day all the adult super heroes simply disappeared. No one knows the cause, as far as all the young supers who remember the old world-- every one would attest that they just woke up one day and all their mentors and commanders were just gone. In fact, all of the adults that remained in the world seemed oddly oblivious to the chaos that had taken hold of their world for so many decades. It was as if all at once only the sidekicks and youngest of the evil-doers remained.
Suddenly all of the safeguards that protected the world from the worst of super villains have disappeared leaving it prey for even the most inept villainous kid and all of the sidekicks can no longer rely on anyone but themselves to solve the problems.
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Basically this is a mash-up of Teen Titans and Young Avengers or New Mutants, with the rules of engagement being based on cartoon/comic book logic. All of the adult supers-- both heroes and villains-- are just inexplicably out of the picture, allowing the sidekicks to call the shots. So this is a chance to take a minor, overlooked character and give them a real chance to shine.
The supers will be organized into teams-- basically the "Villains" and the "Heroes". The world before the adults went all wonky will be determined by whichever characters are applied for.
I would like to get about 5 villains and 5 heroes to start things out. If I get a couple fewer on either side it isn't a big deal. But I would like to avoid having a large number on one side and only one person on the other since they would likely end up feeling overwhelmed.
Things will be determine free-form. But I cannot emphasize more that you don't "win" this by choosing a character with tons of powers that can take everyone down-- the whole comic balance of "that named character who supposedly has no powers and little training will still put up a good fight and can even win" will still apply. Riddler's daughter can still cause Supergirl problems if they end up battling.
There should also be a fair bit of downtime between missions to socialize with your teammates as well as, under secret identities as students, your enemies. So there should be a lot of potential drama with possibilities of siblings or friends being on opposite sides of the fight and not being aware of it. Inter-personal drama can arise that can affect out the characters work together (or don't) on missions.
By drawing from both Marvel and DC, there is a pretty extensive list of possible characters to choose from, many of which are so barely defined that you could really give them your own twist.