So here's the circumstances cause there's gotta be specifics right? You can enter the world of any video game but only as a sort of side character to the existing main character, and you'd be a new one, not an existing one. Example if you did Halo, you may be another soldier working alongside Master Chief, or Assassin's Creed you'd be a fellow member of the Brotherhood. And whatever you are has to work logically with the lore of the game. Example, in Dishonored only 8 people at a time can have the mark of the Outsider I believe, so you'd likely be a normal human being. I can't really decide myself.. definitely not Dead Space for one. As of now assassins creed seems neat..