During the tribal phase of the game, the tribes vie for the ownership of the Immunity Idol. The winning tribe will be granted safety from the upcoming Tribal Council.
In rare cases, there are double eliminations where both tribes go to Tribal Council, where the Immunity Idol is temporarily retired and is replaced with the Immunity Necklace which is usually only available post-merge. After this double elimination, the tribal Immunity Idol is back in play until the merge.
In Survivor Fan Characters 2: Brains vs. Brawn, the first post-merge Immunity Challenge involved the castaways being divided into two teams, and as such the tribal immunity format was used with the winners of the challenge being abstained from Tribal Council.
After the merge, where there is only one existing tribe, the remaining contestants compete in individual challenges to seek possession of the Immunity Necklace, which guarantees safety at Tribal Council for its bearer. Unlike the tribal Immunity Idol, which gives exemption to an entire tribe, the incumbent wearer of the necklaces still must attend Tribal Council and cast a vote, but that player cannot be voted out. Individual immunity is transferable, giving safety to its new wearer, while leaving the original winner vulnerable.
On some occasions, Individual Immunity has been played for during the pre-merge stages of the game, usually occurring during a Double Tribal Council. It can work one of five ways:
An Individual Immunity Necklace appears at a certain location on the island. The first members of each tribe to get to them are granted Individual Immunity in some form. (Survivor Fan Characters: All-Stars)
There has been one case where no one post-merge has come to Tribal Council with immunity. During Survivor Fan Characters 8: The Midway Island, the contestants gave up immunity in the first individual immunity challenge, resulting in no one having immunity. Xero was voted out.