A lot of assumptions... The DLC supposed to continue the plot after the game ending is Resurrection and not Reverie. I think Reverie takes place during Gabriel's quest at some moment after Carmilla's defeat but before the final battle against Satan, probably even before Gabriel's travel to the land of the necromancers... Time traveling?... I really doubt so, the clock device most be a new puzzle to solve during the mission... About the evil who was freed when Camilla was defeated, hmm... Can be anything, the castle was haunted before Carmilla's arrival and she suppressed the evil presence when she took the castle... Could be Frankenstain's moster but also another evil presence is possible... Doppelganger or Legion?