At first glance, The Devil’s Nightmare looks like a shoo-in addition to the Shitty Movie Sundays Watchability Index. After a full viewing, however, I can say that it’s not. And since Missile Test is a dictatorship, my opinions have the force of law.
The main reason why one would think this is shitty is that the movie doesn’t look all that good. It doesn’t appear to have ever gotten a restoration before release to Blu-Ray, and, as of this writing, it wasn’t available on streaming. The print I saw was from a horror compilation DVD set, formatted for CRT televisions.
Next is the dubbing. The Devil’s Nightmare was a joint Belgian/Italian production. Whoever handled the English-language dubbing found passable voice actors, but the sound is dreadful, with many lines featuring heavy distortion and static. Whoever owns this film has been a poor steward, letting it rot to the point where initial impressions are bound to be negative. Get past that, and a viewer will find a decent horror flick.
Released in 1971, The Devil’s Nightmare concerns a curse that afflicts the von Rhoneberg family. They’re old European nobility. Centuries ago, one of them made a deal with the devil (who is a character in the film, played by Daniel Emilfork). The devil extracted a heavy price. In every generation of von Rhonebergs, the firstborn daughter will grow up to be a succubus, trapping souls for the devil.
The last surviving Baron von Rhoneberg (Jean Servais), thought he solved that problem for the latest generation by murdering his newborn daughter in her crib at the tail end of World War 2. But, if he had pushed the succubus down to another generation of von Rhonebergs, we wouldn’t have a movie.
Back in the present day, 1971, a busload of tourists finds their path through rural Belgium (maybe it’s supposed to be Germany) blocked by closed roads. They need somewhere to stay for the night, and the castle of the von Rhonebergs (played by Antoing Castle) is the only place that can take them in for the night. The baron is accommodating, 
and the guests are all shown to their rooms by the most dour of butlers (Maurice De Groote).
The tourists are: redhaired Corinne (Ivana Novak), blonde Regine (Shirley Corrigan), the curmudgeonly Mason (Lucien Raimbourg), priest-in-training Alvin Sorel (Jacques Monseau), husband and wife Howard and Nancy (Lorenzo Terzon and Colette Emmanuelle), and tour guide Ducha (Christian Maillet). Each of these characters, and this is the clever bit, are embodiments of the seven deadly sins. As one would guess, each of them becomes the target of the succubus, and how they die (or don’t) relates to each of their mortal sins. As for the succubus, the film holds no mystery about who that is. The succubus is Lisa Müller, played by Erika Blanc. She appears at the castle after everyone has sat down to dinner, and joins them wearing an outfit that makes the Fleabag jumper look boring by comparison.
After everyone heads to their rooms to settle in for the night, they are all visited by the succubus, and the cast is whittled down. How some characters relate to the sins isn’t perfectly clear. A couple are a reach, but watching the succubus ply her trade was the most satisfying part of this film. Director Jean Brismée created some surreal vignettes that confuse time and space. There is some nice cinematic trickery in a couple of these scenes, and one, involving gluttony, that is a masterclass in grossing out an audience. It’s an impressive scene for being devoid of blood and gore. Viewers who are bloodhounds will get a mild red fix elsewhere in this movie.
There are parts of this film that are ridiculous. Also, even though the performers are all dubbed, so judging their actual readings is impossible, there are a couple performances whose weakness passes the language barrier, notably Monseau and Raimbourg. But, Blanc, who one might expect to be nothing but a pretty face, did very well in her role.
I’m not sure this film will find much cachet amongst those who are not into horror films. But for those, like myself, that hoover up horror flicks throughout the year, it should be a pleasant surprise.