You were going about your life, when suddenly a portal appeared. A hand stretched out of the portal and hit you with a club. Next thing you know, you're tied to the inside of a wagon with metal chains.
In this game, your characters will be expected to come from a variety of universes. Be they fictional, real life, or vague and ill-defined. This world has different laws of physics, and different laws of magic than most others, so a magic user or athlete from another dimension may have their skills reduced or increased, depending on the individual. Anything a character says about their home universe is automatically canon.