Soooo, my crazy theory is that Reginald is kind of meta-aware - considering how he comments on experiencing things many times over, the way he always conveniently shows up just at the right time and that he understands Mary with her mouth taped (or not Mary, but the player directly??), I'm thinking that he somehow knows different routes of the game and has experienced them many times. Maybe that's why he's a little insane and doesn't care about dying/killing people.
But that doesn't really explain the eye/symbol thing. When you bring it up with him, he gets worried, and tells Mary not to think about it if she doesn't want to end up like him, so I'm guessing that... thing is what gave him the awareness/route-skipping power. But then, why does he say not to worry about it? Wasn't it Reginald who left the symbol and the note inside the manga for Mary to find? Also this force seems to have its own agenda, even working against Reginald, breaking the rope when Mary was tied up at Reginald's house. Why would it interfere? Just for fun?
Also, who the heck was in that coffin at the church? Were they buried below that gravestone with the symbols on it? How are they connected to Reginald?
So many questions, so little answers...