My Bloody Valentine (1981) | HORROR/SLASHER | FULL MOVIE

On Valentine's Day 20 years before, an explosion of methane gas took the lives of a group of coal miners working in the Hanniger Mine near the small Nova Socia town of Valentine Bluffs. The accident occurred because supervisors left their posts to attend the annual Valentine's Day dance. A year afterward, Harry Warden - the only survivor of the accident - retaliated by killing the two supervisors, and leaving a terrifying warning never to hold another Valentine's Day dance. Now, a group of young adults decides to hold another dance, despite warnings. When a blood-soaked heart arrives at the police station, accompanied by an ominous message, the dance is canceled. But a Valentine party is held in its place... at the coal mine, and it isn't long before the town's young people begin dying violently. It appears Harry Warden has returned to punish those who did not heed his warning.

IMDb: https://www.imdb.com/title/tt0082782