Factual error: The priest says that St. John saw the number 666 in his vision, but it was actually 999 inverted. St. John wouldn't read modern Arabic numerals like we do, it would be Roman numerals. The number 666 would actually be DCLXVI. (01:05:40)
Factual error: As the subway trains are disconnecting, Arnold fires a 203 grenade launcher at Satan, knocking him back onto the other train. A 40mm grenade doesn't arm itself until about 15-25 meters, so unless Satan jumped extremely far, the round would not have detonated. (01:43:05)
Factual error: Arnold's wife and daughter are shot once each. There should not be blood on all four walls of the room.