The Imposters is a twist that appeared in Survivor: Puerto Rico. The idea behind the twist is to trick the cast, so that select castaways revealed at the beginning of the season are later unveiled to be fakes, but not before they have had an impact on tribe dynamics.
The imposters are selected before the cast is revealed and bundled in with the real castaways during the cast reveal to make them seem like actual cast members. After a pre-set amount of time, following their integration into the game but before it has started, it is revealed that there are imposters within the game. All the real castaways then vote for the person they think is the imposter. The tribe that has the most correct guesses for their imposter receives an advantage in the first immunity challenge, while the tribe with the least correct guesses gets a disadvantage. The imposter with the least votes also gets to decide the merge immunity challenge.