First things first: although the name 'Alucarda' spells 'a Dracula; backwards, this film has nothing to do with vampires—it's simply the name of one of the characters, whose parents obviously didn't consider the possibility of bullying at school (not that the young lady cursed with such a silly moniker would have have stood for any nonsense from her peers: like Stephen King's Carrie, Alucarda is able to deal with those who vex her in spectacularly fiery fashion).
What the film does offer is demonic possession, strict Catholicism, nudity, self-flagellation, lesbianism, torture, orgiastic sex, and more screaming, wailing, and fainting than in the front row at a Take That concert. In short, its a prime slice of 70s nunsploitation, served up Mexican style ie., it's surreal, bloody, and more than a little bit bonkers (not surprising, I suppose, since it was directed by Juan López Moctezuma, the man who produced Alejandro Jodorowsky's equally insane El Topo).
Mixing elements borrowed from The Exorcist, DeSade's Justine, Ken Russell's The Devil's and the aforementioned Carrie, Moctezuma's medley of Mexican madness sees the titular character (played by menacing brunette Tina Romero) seducing pretty young blonde Justine (Susana Kamini) after she joins the convent at which Alucarda is staying. The two girls form a close bond, making a blood pact to die together, and eventually allowing themselves to become host to a demon (or possibly the Devil himself). This obviously upsets the nuns, who call for an exorcism. which in turn, upsets Alucarda. Cue flaming nuns, a collapsing convent, and a whole lot of histrionics!
Amongst the general lunacy, and the incessant screaming, the film offers these particular delights to those with a taste for the truly bizarre: an old hag with more straw in her hair than Worzel Gummidge; a gypsy who is the dead ringer for TV's Catweazle; nuns wearing dirty ra-ra habits (which are like a ra-ra-skirt, only full length, with a cowl, and dirty); a knife made from the tear of a gypsy girl (?!); an orgy attended by women with more hair than Cher, Tina Turner and Amy Winehouse combined; the exchange of blood during a Satanic ceremony; a reanimated dead nun being beheaded; blasphemy during a bible class; death by holy water; and lots and lots of nekkidness.
If that sounds like your cup of tea, and you think you can endure the wall-to-wall cacophony of screams, I say 'go for it'; the film proved a little too avant garde (and noisy) for my taste, but if nothing else, it was certainly a unique experience.