What's Earth-30847? Simply put, it's one of many of Marvel's alternate realities that crosses over with another property or properties, much like Earth-7642.

In this case, this particular iteration of Marvel's Earth takes place within the Marvel vs. Capcom series, which while the circumstances of both sides' interactions different depending on the game, the core concept is the same; a world wherein Marvel characters and Capcom characters coexist, come into conflict, save lives, and cause LOTS of property damage.

Let's hear those headcanons, drop a drabble or two, and have fun!