I've seen horrors... horrors that you've seen. But you have no right to call me a binge-watcher. You have a right to kill me. You have a right to do that... but you have no right to judge me. It's impossible for words to describe what is necessary to those who do not know what horror means. Horror... Horror has a face... and you must make a friend of horror. Horror and moral terror are your friends. If they are not, then they are enemies to be feared. They are truly enemies! I remember when I started with this evil list... It was called extreme, surreal and bizarre movies of some interest, seems a thousand centuries ago. There was this movie. They went into a camp to inoculate some children.They left the camp after they had inoculated the children for polio, and this old man came running after them and he was crying. He couldn't see. They went back there, and they had come and hacked off every inoculated arm. There they were in a pile. A pile of little arms. And I remember... I... I... I cried, I wept like some grandmother. I wanted to tear my teeth out; I didn't know what I wanted to do! And I want to remember it. I never want to forget it... I never want to forget. And then I realized... like I was shot... like I was shot with a diamond... a diamond bullet right through my forehead. And I thought, my God... the genius of that! The genius! The will to do that! Perfect, genuine, complete, crystalline, pure. And then I realized... I realized these movies were stronger than me....

~Kurtz, Apocalypse Now

After meandering an expected 20.000 minutes through the most extreme movies ever made, there is finally some relief. A less extreme moviescape, only to mercilessly plunge back into extremeness, but this time a new kind of almost structured extremeness, slowly descending in periods of bliss and absolute terror... You've been warned....

With the possible exception of a few listed movies I've seen and liked, I don't recommend anything. The credit for this list goes to Zev Tolenado, and his web site thelastexit.net.

Besides categorizing extreme movies as 'recommended', 'of some interest' or 'worthless', he reviews each movie too. Only the 'of some interest' listings appear in this list. Here are the recommended. I'll quote a line from his introduction:

This is an encyclopedia of fringe, surreal, bizarre, extreme, twisted, offbeat, splatter and shock cinema, including freaky arthouse, intense cult/midnight movies, and works by Dadaists and Surrealists

All listed movies are reviewed on the last exit.

Extreme (1-215) (recommended)
Borderline Extreme (216-504) (r)
Old Movies (505-537) (r)
Asia (538-578) (r)
Europe (579-689) (r)
Japan (690-733) (r)
Russia (734-743) (-)
Surrealism (744-776) (r)
Counter Culture (777-820) (r)
Everyone Else (821-893) (r)

Stuff I couldn't find on Letterboxd:
-Sami (2001)
- La sensualità è un attimo di vita (1975)
-Cheonggyecheonui gae (2009)
-cinema abattoir
-Eliza's Horoscope (1975)
-Nouvel ordre (2006)
-The Flew (2008)
-The Grateful Undead (2007)
-Hic Digitur Dei (1976)
-Karnabal (1985)
-Kraftverk 3714 (2005)
-Lezione 21 (2008)
-Le nécrophile (2004)
-The Performance For... (Yuri Kiyashko)
-Plastic Utopia (1997)
-Kyuketsu (2011)
-Spike and Mike's Sick and Twisted Festival of Animation: Caught in the Act (2005)
-Spike and Mike's Festival of Animation Sick & Twisted Volume 4 (1997)
-Spike and Mike's Sick and Twisted Festival of Animation Volume 7 (2000)
-Spike and Mike's Hilarious Sick and Twisted Festival of Animation (1997)
-Spike and Mike's Sick and Twisted Festival of Animation 1998 (1998)
-Dalí (1991)
-Gums (1976)
-Leolex (2013)
-Through the Looking Glass (1976)
-Lo que vendrá (1988)
-Villemolle 81
-Ten Courts of Hades (Lo Chi)
-Terrorama!
-Q smette di ricordare (2013)
-Io... donna (1971)
-Creature 2013 (2013)
-Goodbye, Little Betty (2013)
-Regissören (2011)
-Video Geisteskrank (2008)
-My Monster (2009)
-The Dead Have Risen (Charles E. Cullen)
-Mr. Stitches (Charles E. Cullen)
-The Short Films of David Lynch (2002)
-Tales of the Valley of the Wind (2009)
-I Am Nightmare
-Spooked (2007).