According to New Advent - here is a list of Anti Popes (Certainly not all inclusive.)
A false claimant of the Holy See in opposition to a pontiff canonically elected. At various times in the history of the Church illegal pretenders to the Papal Chair have arisen, and frequently exercised pontifical functions in defiance of the true occupant. Hergenröther enumerates thirty in the following order:
Hippolytus (?), III century
Novatian, 251
Felix II, 355-365
Ursicinus, 366-367
Eulalius, 418-419
Laurentius, 498-501
Constantine II, 767
Philip, VIII century
Anastasius, 855
Leo VIII, 956-963
Boniface VII, 974
John XVI, X century
Gregory, 1012
Sylvester III, 1044
Benedict X, 1058
Honorius II, 1061-72
Guibert or Clement III, 1080-1100
Theodoric, 1100
Aleric, 1102
Maginulf, 1105
Burdin (Gregory VIII), 1118
Anacletus II, 1130-38
Victor IV, 1159-64
Pascal III, 1164-68
Calixtus III, 1168-77
Innocent III, 1178-80
Nicholas V, 1328-30
Robert of Geneva (Clement VII), 20 September, 1378 to 16 September, 1394
Amadeus of Savoy (Felix V), November, 1439 to April, 1449
Now an Anti Pope is distinguished from a False Pope in that in the case of an Anti Pope there is a legitimate Pope simlutaneously. However - today due to the Nature of the Heresy of Modernism and the Global goals of the Progressive movement - we currently have a situation where we should at least question the Validity of the Post Vatican II Claimants mainly because of the numerous questionable actions we have all witnessed that have resulted in the SSPX Movement and the Sedevacantist Movement.
I pose the question - Why are some of us so quick to assume that an Anti Pope or False Pope cannot usurp the Papacy in Our Time?
Matthew 7 15 to 20 clearly states that we are to beware of False Prophets. St Paul likewise exhorts us to not entertain prelates who bring us doctrine not in keeping with the Doctrine he Brings. With all these warnings - why do people think that Catholics today have to have blind obedience?