KMC Forums - need help with finding a movie...

Desperatly searching for a horror movie I watched as a kid. It most likely
sucks and is obscure, but it scared the shit out of me when I was a kid and
I'd like to renew the memories...The things I remember:
It's most likely from 80s or early 90s, possibly even earlier...It's about a
bunch of teenagerswho find a medallion. It has strange powers and a group of
deformes humanoid monsters in a crypt need it to resurrect a demon/monster.
I remember a scene where one of the teenagers runs through the woods, a
police car comes by but instead of the cops it's one of the monsters inside.
It takes the teenager through the window and drives away...In the end the
demon is resurrected and destroys a police blockade...one of the monsters is
killed when the kids put his head in some acid or similar stuff - only the
backbone remains where the head was once....That's about all I can remember.
I hope some horror freak will be able to help me with the title. Thanx in
advance!