A lot of these types of games involve team work, but among the group is a player whose job it is to stop the others from accomplishing their objective. All players start the game knowing someone is "it", they just don't know who.
There are also games that acquire a player to become "it" during a game changing their objective mid game.
Then there are the games that act as co-op, but at the end your objective is to win...not as a group but as a player, whether you are "it" or not.
THIS game starts with all players working together as humans. There is NEVER a player who could be the Thing. Players work together because when one human wins...they all win. However, as the game moves forward, the odds of a player becoming the THING begin to grow. The more chances a player takes, the more he could become infected. By the end, everyone wants to believe they are who they started as...but vulnerability is man's concern.