The Japanese Guinea Pig series of movies, particularly the first two, are exceptionally gruesome. The first one, Flower of Flesh and Blood, only has one death scene, but it’s 90% of the entire movie. A woman is kidnapped, given a drug to paralyze her and slow her heartbeat, and then methodically snipped, sawed and hacked into pieces for the next 45 minutes. It’s so realistically done that for a while it was believed to be an actual snuff film.
The later videos in the series are played more for laughs. The second film The Man Who Couldn’t Die, now that I think about it, shouldn’t even count, since nobody dies. A dejected loser decides to end it all, only to find that he just can’t die. He then spends the rest of the film ripping himself to shreds.
Also, the wheel of skin from Jisatsu Saakuru (Suicide Circle) was more disturbing than many film deaths I’ve seen.