If you want a unique and inspired Halloween costume that leaves people wondering at the meaning and greatly unsettled, there is no better way than to look to Native costumes and Pagan ceremonial costumes to find some very creepy ideas -
Straw, fur, antlers, masks with paper mache, rags, burlap, pitchfork, leather, hay, rope....
Think in terms of materials used by people in remote areas, raw, lots of texture, no colors....
I hope this inspired you to consider utilizing elements you have around your home; cheesecloth, chambois, burlap, flour sacks, fur, antlers, throw rugs, blankets, pillowcases, bark, straw, twigs for antlers, and more.
Remember, homemade leaves the viewer to fill in the "what is it?" with their own imaginings. Instead of just putting on a Batman costume and being one of a thousand other Batmans whose story we know, dare to be something vague.
Vague is very effective.
Here's some examples -