Reverse & Revoke is a twist that featured in Survivor: Jan Mayen and again in Survivor: New Zealand and Survivor: Entitled vs. Earned for a one-off stint. It flips the pre-merge game on it's head so that players are forced to vote before they compete in the Immunity Challenge.
On each designated Reverse & Revoke day, all castaways are required to send in votes for who they wish to be voted out from their current tribe, with the votes being read pre-challenge. The tribe that then wins the subsequent Immunity Challenge get to decide weather they should keep Immunity, revoking the vote they did pre-challenge, and sending the person the other tribe has voted for home. Or, alternatively, give immunity to the other tribe, revoking the vote the other tribe did, and sending their own person home that they voted for instead. It is up for them to decide to if they should keep Immunity for numbers, or give it up to oust someone they don't like. This twist forces people to vote, so there is no way to avoid Tribal Council and avoid having to make tough decisions. This becomes even more important when you are aware the person you are voting for may still survive the vote.