Other mistake: In the scene where Cyrus's Nephew first sees the kids in the in the machine. (1:18:45) The shot goes back and forth from him to the machine. The first 2 time the glasses are fine the last shot (1:18:550 The prescription inserts in the glasses are crooked. Bad editing. (00:18:45 - 01:18:55)
Other mistake: When Maggie puts the "magic" glasses for the first time, you can see that the light in the right (left to us) lens sparks and then turns off. In the next scene it works fine. (00:31:21)
Other mistake: When everyone is looking for Bobby, Matthew Lillard says that it is no use shouting because the glass is 100% sound proof. Yet when he is trapped in the cage, he hears Maggie screaming directions for him to dodge the ghost - not sound proof at all then.
Other mistake: When Dennis jumps out from behind the glass wall shield, leaving Arthur behind it and The Hammer and Juggernaut ghosts attack, Arthur bangs the glass yelling as if he can't get out; but the wall shield is only propped up, unsupported and should've fallen straight forwards when he thudded his fists on it.
Answer: He's alive. He faked his death at the beginning of the movie to get Arthur and his children into the house, because only then would he be able to force Arthur to engage the 13th Ghost. When Cyrus is seen at the end of the movie, he is disguised with the blood patch to make it appear that he is dead to a casual observer with the glasses (everyone is wearing them at this point) and prevent Arthur from being able to figure out his plan.
Phoenix