Who dictates if a pope is an anti pope or false pope?

Answer 1

Catholic AnswerAs there hasn't been an anti-pope since the fifteenth century, I think we don't have to worry about this so much. The Cardinals are the Bishops who are responsible for electing a new Pope, and if there is someone claiming to be Pope who was not elected by the Cardinals and is not ruling in the Vatican, then I think it would be pretty obvious to most people. The only time there was a real problem was in the fourteenth century when the Pope had moved to Avignon, France for a number of years, and there was an anti-Pope elected in Rome while the real Pope was in France. Before the whole mess got sorted out, there were three claimants to the Papal throne, they all ended up resigning and a new Pope was validly elected. For a complete list of popes, along with the anti-popes see the link below.