'Plastic Wives' Star -- My Ex Is Like Satan!

"Plastic Wives" star Frances Marques says her ex-husband threatened to kill her ... and looked like he was possessed by the devil while trying to do her in.

Marques -- who stars on the show with her ex, Dr. Ryan Stanton -- claims he went berserk last month at his Bev Hills office when she tried collecting rent ... calling her an "old ugly c**t."

In her court docs, Marques alleges Stanton takes "loads" of steroids ... and fears his rage will cause him to shoot her and her daughter. She says everyone at his office is afraid of him.

A judge gave her a restraining order ... but he only has to stay 10 yards away, so it's iffy protection.