Another film so bad it's good I'd recommend from memory (though it's inexplicably regarded by some gore hounds) is Dèmoni (1985) aka Demons directed by Lamberto (son of Mario...the director not the computer game plumber) Bava but probably more famous for being produced by Dario Argento.

Best watched badly dubbed.

I used to bore my friends to undeath making them watch Argento movies (a pastime I still find myself defending to this day).

The plot is uttely inexplicable involving films within films, Lovecraftian plot hinges etc but it's your basic pretty Italian people turning into yellow puss filled monsters story.

SPOILERS, IF YOU WANT TO WANT TO ENCOUNTER THE FULL IMPACT OF THIS FILM DO NOT READ ON...

All rather hum, drum (and for what happens next to work it really needs that pacing) until our remaining heroes are caught in a utterly inescapable position and suddenly...

...well let's just say if you want to explain the phrase 'deus ex machina' to someone you need look no further but it really is executed with such surprise and panache (which I've hopefully not destroyed by what little I've divulged) and lack of any prior plot telegraphing that it's as entertaining as Divine being raped by a giant lobster in Multiple Maniacs (and that's saying something).