Unseen Evil (2001)

"If you see it, you're dead."

A group of hikers led by a college professor are searching the woods for an ancient Indian burial mound. When they discover a likely site, three members of the group reveal themselves to be grave looters, and tie up the others so they can keep the valuable artefacts for themselves. In the course of ransacking the mound, one of them stumbles across a cursed crown that unleashes the mound's guardian: an invisible monster that begins attacking everyone it finds. Will anyone make it back to civilization alive?