How did Troy even get Archer's face? He's one guy. As I remember it, he wakes up, the medical and police team has an Oh Crap moment and next thing we know he's got Archer's face. He's one guy. They would have had to sedate him to put the other face on. Castor has no resources there, and he's just a regular human, why didn't anyone just strap him down again while he was sedated?
He wasn't one man. He'd called in his friends. They're the ones that actually haul Dr. Walsh in. You're misremembering how the movie went.
This continuously bugs me: after the switch is made, Castor-as-Archer goes home to the "lonely wife," Eve Archer. It is implied through foreplay and dialogue that the two did sleep together physically in the same bed and have sex. Wouldn't Eve known something was immediately wrong by reasoning that Archer did not..."feel" the same way as she would expect?
Perhaps she would, but it's not like one night of different sex would make her immediately suspect her "husband" was actually Castor Troy in a freak surgical disguise. Plus, notice that Castor looks in Archer's diary and reads that they haven't been getting it on much recently (as in not in the last two months, to which Castor quips "What a loser"), so she may just chalk it up to remembering poorly.
I expected there to be a Chekhov's Gun about his lack of scar being how she identified him either before or during said lovemaking.
Castor may have explained the lack of scar simply by saying that he got plastic surgery while he was away, which is, twistedly enough, the truth.
How the hell does Castor get away with shooting Agent Loomis when Pollux gets killed? I know the ballistics might have taken a while to do, but Castor uses his FBI duty pistol to headshot Loomis, which should have been easy to trace. And I can't even remember if Pollux had a gun on him at that point.
Actually Pollux did have a gun. You can see him raise it as Archer swings over on the rope and he is about to shoot when Archer slams into him and knocks him into the skylight, and he falls to his death.