The Mole - A Fun Add-On For Teenage Team Games
One playing card is dealt to each person before group activities (making sure one of the cards is the Ace of Spades). The person who gets this card is called "The Mole". The group of people playing is divided into two or more teams. Through the rest of the party all games played should be team games, and should use the teams chosen. The job of the mole is to make sure his/her team loses. They should, however, try to avoid suspicion, as every 10 minutes all players will get a chance to guess who the mole is.
If many games are going to be played, then the best way to keep track of the mole's evil doings is to keep a tally of how many games are won by each team. If only one game is to be played, then simply keep track of the cumulative scores.
Every ten minutes (you could extend this time if you want), each player should find a place to be alone, preferably in separate rooms with doors. Then, all players should go in order and announce if they'd like to make a guess as to the mole's identity. If they do, then they go to where their guess is hiding, without letting anyone else see who they walk to, and ask if they're the mole. If they are not, the player asking is out, if they are, the game is over and the player asking wins.