evil dead (1981)

aka Book of the Dead. Into The Woods. Sam Raimi's The Evil Dead. The Evil Dead, the Ultimate Experience in Grueling Horror.
Five friends holiday in a backwoods cabin. Unfortunately there is a malevolent spirit loose in the woods, which they unleash when they find the Necronomicon, (a book of the dead), and its translation. One by one, they succumb to the evil, leaving one trying to survive till morning.
Once the action gets going this is a truly harrowing, and completely unrelenting horror. But it also knows how to relieve the tension with some deeply black humour. The film became one of the original video nasties, it features the notorious tree rape scene, that viewed now is far less harrowing than in 1981. This is a masterclass in how to make an effective horror with little money.