During the flashback to 1692, as Father Andrew is getting murdered, they show his feet are shown flailing about. Problem is the materials (e.g. neoprene) used in his sandals would not be invented for another 250 years.
Near the end after all Hell has broken loose the 2 girls run out of their rooms and Ann is wearing a 1 piece nightgown that is off white, when one of the men come back to tell them to get out of the house she is now wearing a 2 piece purple outfit (panties and top).
When Arty is hurled against the ceiling in the beginning, the rig holding him aloft is visible just before his head hits the ceiling in the long shot. The next shot is a closeup of his head and shoulders actually hitting, and the rig is gone.
The goof item below may give away important plot points.
To set up this goof, the following approximate times (in the movie) are needed to establish the timeline:
(16 minutes): Detective Hollister is pulled into the lake by the demon/witch.
(21 minutes): Rev. Maier shows a cross to Rev. Thompson. The cross was extracted from the lake during its attempted draining. After this, all hell literally breaks loose.
(40 min): Elondra (Arlen's mom) tells Rev. Thompson now that the cross has been taken from the pond, they are all doomed. Seems the cross kept the thing at bay where it could only move at night.
This creates a plot hole since Hollister was pulled into the lake, during the day, while the cross was still in the lake. The only reason the cross was removed was because Hollister came up missing and Rev. Thompson wanted the lake drained.