I can't remember this halloween movie.I know its about a boy who gets attacked by a headless horsemen then he has to become some liquid metal technology called a reaxxion. Then the other kids must do war to the headless horsemen so the halloween spirit can be restored.thats all I can remember.

IMDb Search (http://www.imdb.com/find?s=all&q=headless+horesemene)

Try the above and see if any of these ring a bell. There are numerous/similar films