Smash: World of Decay

In the World of Smash, one fateful day a series of spherical bombs were set off across the land. They left in their place massive gaps between this world, and another: Subspace. But with it came a virus of dark matter, it spread rapidly.
Four months later, the ones strong enough to fight their way through this new world of decay are brought together by fate. They must battle to uncover the secrets of what led to this virus spreading, or succumb to it in the process.

(Okay, since Smash is a big crossover, setting a story in that world can get a little confusing so I'm just clearing it up. The main world is a combination of all the Nintendo series, Mushroom Kingdom, Hyrule, Dreamland etc all exist in this world. Third party characters exist independently from this world, it gets explained later. Characters from the same series know each other and have pasts together (ex: Mario & Peach) but others (ex: Link and Samus) do not.