No film, let alone trailer, that’s un-spooled in theatres this year generates quite the laughter that the preview for “Bones” always elicits. With Snoop Dogg uttering the oh-so-quotable would-be bad-ass line “I’m on a natural high. A super natural high,” the ad for Ernest Dickerson’s urban horror film promises lots of unintentional hilarity.

For most of its run time, though, “Bones” isn’t quite as much fun as that abbreviated taste. In fact, for a good hour the top-billed rap superstar is barely featured. Aside from a couple of flashbacks, including unintentionally comic retro-Blaxploitation title sequence where his inner city entrepreneur character Jimmy Bones struts the streets all pimped out in a pinstriped suit, Snoop is relegated to veritable cameo status for the first two acts. “Bones” begins as a weak haunted house picture that is more cheesy than flat-out awful. The house in question is a disheveled old ghetto brownstone that a none-too-bright young man named Patrick (Khalil Kain) decides to turn into a nightclub. Little does he know that the building is not only where Bones was murdered back in 1979, but it is also where his very pissed off spirit resides. Furthermore, little does Patrick know that his businessman father Jeremiah (Clifton Powell) played a major role in Bones’ brutal end.

Dickerson spends this first hour trying to establish a somber and serious horror movie tone, and rather surprisingly he actually has some success in spots. The effects work used to depict the Bones ghost is convincing if not exactly scary, and there is one dream/psychic vision sequence that registers pretty high on the creepy scale. But any efforts to create a convincingly horrific atmosphere are done in by the terrible dialogue and poor plotting by writers Adam Simon and Tim Metcalfe, not to mention the wretched efforts from his cast, particularly a still-slumming Pam Grier (why oh why is she getting such bad parts after her memorable career-reviving turn in Jackie Brown?) as Bones’ psychic former love Pearl.

But Grier has nothing on Snoop, who finally enters the picture in some substantial way for the final act. As soon as the dramatically challenged Snoop takes center stage, gone are any traces of attempts at a serious thriller, and “Bones” suddenly morphs into an intelligence-insulting ghetto version of “The Crow” that makes up its new supernatural rules as it goes along. With the shift, Dickerson throws up his hands and surrenders to full-on camp: a talking severed heads becomes a wisecracking comic sidekick; people cower in fear before Snoop, who with his soft voice and flamboyant pimpwear is far from intimidating figure of horror he’s supposed to be; that his would-be cold-blooded pre-killing one-liners are howlers of the highest order certainly doesn’t help. Nothing sums up “Bones” better than its parting shot, in which maggots are projectile vomited directly toward the audience. How so very appropriate.