When did horror movies become so gentrified? Right this minute there are more talentless hacks churning out by-the-numbers horror flicks for Hollywood than there are bank branches in the East Village. Directors such as David Cronenberg are rejecting their horror roots to make middlebrow art-house fare, and on the screen the once-transgressive shockers of the 1970s and ’80s are being remade as glossy teen flicks where the dirt and gore have been replaced by nontoxic Hollywood grime and computer-generated ghosts The horror movie ghetto has been cleaned up, hosed down with disinfectant, and filled with condos.

But one grimy corner of the East Village is staging a last stand this month, and its weapon of choice is filthy, independent horror. The Pioneer Two Boots Theater will be pumping out its gloriously disreputable “Fourth Annual Month of Horror, Terror and General Mayhem,” and it’s a festival of poisonous filth, a piñata of pus, a celebration of crud. In American movies, dirty equals scary, from the filthy cannibals of “The Texas Chain Saw Massacre” to the bleeding walls and un-renovated basement of “The Amityville Horror,” but filth is also fertile, and in the mucky corners of indie horror, you’ll often find gold.

But first you’ll have your sensitive palate bombarded with a fusillade of bad taste. There’s direct-to-video garbage such as “Wrong Turn 2” (a sequel no one demanded) and the Ronald-Reagan-versus-hippies gut-cruncher “The Ripper,” directed by David Arquette,, and starring Lukas Haas and Balthazar Getty. Then there’s the no-budget, glue-sniffing headache of “Stupid Teenagers Must Die” and the slasher-film-cum-concert movie “Punk Rock Holocaust.” There’s even a screening of “Tintorera” the sleazy, soft-core Mexican version of “Jaws,” upholstered in wall-to-wall disco, that’s been scientifically proven to cause actual brain damage.

But pearls grow from a speck of grit, and there are treasures aplenty down here among the shoestring budgets and shot-on-video gore. Simon Bisley’s “The Living and the Dead” is a gothic abuse saga that kicks off when Lord Brocklebank leaves his majestically decrepit family manor on business, entrusting his invalid wife to the care of their inbred, upper-class twit of a son. The weak-chinned schoolboy decides he knows what’s best for mother’s health: Half the audience will be hypnotized by his depraved attempts at nursing, and the other half will run for the exits.

Ti West’s “Trigger Man” rejects narrative, character, and back-story to wring horror from nothing more than its setting as a group of Brooklyn hipsters go deer hunting. It’s a low-budget twist on a Michelangelo Antonioni film, with its trucker-cap-and-tattooed trio walking through the peaceful forest in real time until the sylvan silence is shattered by high-caliber rounds that shear off the tops of their skulls. Atmosphere is everything, as the lush, life-giving forest falls away to reveal a rusted, burnt-out factory in its heart, home to a pack of silent snipers.

The scummiest movie of the month, however, is also the most well scrubbed. Gregory Wilson’s “The Girl Next Door” is set in a 1960s suburbia and is shot in Easter egg pastels, as lovely as a basketful of kittens. But this is the anti-“Stand By Me” where no one does the right thing and acts of gallantry come far too late. Ruth Chandler (Blanche Baker) is a single mother raising three boys, whose orphaned niece, Meg (Blythe Auffarth), comes to live with her. Ruth encourages her boys to torment Meg and childhood games soon darken into all-out torture. Hyper-stylized, “The Girl Next Door” is dominated by Ms. Baker’s ferocious performance, as magnificently monstrous as Faye Dunaway’s portrayal of Joan Crawford in “Mommie Dearest.” But those expecting campy fun should stay home. The image of a 1960s housewife standing over a sobbing, teenaged girl and wielding a blowtorch will scar you for life.

There’s also an unexpected masterpiece among all this mayhem. Coming across Brian Springer’s “The Disappointment: Or, The Force of Credulity” on the same bill as “An American Werewolf in London” is like discovering Errol Morris’s “The Thin Blue Line” playing a double feature with “Barn of the Naked Dead.” A personal documentary about one man’s obsessive hunt for buried treasure, directed by his son, “The Disappointment” more than a little messy, and it features a narrator whose voice is as soothing as nails on a blackboard, but it’s also an inspired work of psychic history.

A cave rumored to hold buried treasure. A farm owned by an early American anarchist whose diaries have been lost. A mysterious rock carving. A fraudulent Indian artifact. “The Disappointment” uses these four elements to tell an all-American story about napalm, spirit possession, Korea, Vietnam, American Indian massacres, early American opera, lynching, fanatical obsessions, 200 tons of dirt, and the way mothers try to protect their families from wounds that never heal. Most devastating of all, the film speaks compassionately and bluntly about veterans who return from war and spend the rest of th eir lives with one long scream echoing inside their skulls. This powerfully affecting documentary is just one way to say “happy Halloween” from the messy, inspired, fertile, fantastic, trashy heart of the dirty old East Village.

Through October 31 (155 E. 3rd St., between avenues A and B, 212-591-0434).