So if Mark orchestrated all of this just to punish his friends, I guess the next question would be: What was he revenging?
The current theory going around was that Celine’s affair with the Colonel resulted in her having his baby (hence the crib in the bedroom), while she and Mark were still married. And that Mark, due to the influence of the entity in the house, became angrier and angrier until he snapped.
Damien being one of the victims of his scheme was probably just collateral damage. Which makes that ending even WORSE, when you think about it.
It does leave one huge question on my mind, though… WHERE’S THE BABY?