Deliberate mistake: In the scene with the forest battle, the scene with flaming arrows being fired was filmed on grass (look at the ground) in a separate location, because it wasn't safe to fire them in a real forest. (01:33:25)
Deliberate mistake: Marian is wearing pantaloons, or knickers, in the rape scene. Knickers were not worn by women until Victorian times, and then they were split at the crotch.
Chosen answer: The masked men weren't part of a cult, they were the Sheriff's soldiers, the same ones that Robin meets when he first returns home. They are just in hoods and masks to appear intimidating while trying to kill the noblemen, like Locksley.
Bishop73