I've been trying forever to find this movie. It's more likely an 80s classic horror. A guy and his sister go to a summer camp with friends. I remember that they were making fun of that guy(I believe his name was Martin). He ran into a barn(or something) and noticed something wierd about the lamp in there. Then he burned while looking at it.
The next year, his sister goes to the same camp with the same people. I remember her having nightmares, involving an indian(native American) guy. Then it turned out Martin is actually alive, but extremely disfigured(I guess, because of that burns) and started killing them one-by-one, his sister was planning that with him. In the end, both he and his sister burned in the same barn.
There was scene with his sister taking a bath, she lighted some candles in the bathroom and started saying weird staff I don't remember. At some point, Martin killed a sheriff by tearing his head off with his bare hands. I also remember him coming out of a grave so maybe he was dead after all, but his sister summoned him with a spell of some sort(I'm not sure about that).
If anyone can help, I would really appreciate it!