Absurd (1981, aka: Rosso Sangue, Anthropophagus 2, Zombie 6: Monster Hunter, Horrible, The Grim Reaper 2)
Antropophagus (1980, aka: Antropophagus: The Beast, The Grim Reaper)
Axe (1974)
A Bay of Blood (1971, aka: Ecologia del delitto/ Ecology of Crime, Reazione a catena/ Chain Reaction, Carnage, Twitch of the Death Nerve, Blood Bath)

All Italian films except Axe (US). Antropophagus definitely has the best music/soundtrack. A Bay of Blood is obviously the best of these four films over all, a Mario Bava classic. Absurd is a fairly standard slasher, Axe is similar.