Unfortunately, “Porno” gets more uneven as it goes on, with a somewhat slack midsection and a mix of earnestness, broad comedy, titillation, and moralizing that neither fully gels, nor makes something unpredictably wild out of those clashing elements. Keola Racela’s film gets off to an amusingly self-aware start as youthful staff at an early 1990s movie house inadvertently summon up a real succubus hungry for their bodies and souls. That self-imposed hurdle pales next to the one filmmakers have handed themselves with “Porno,” a comedy horror that despite its XXX moniker (and some gore) mostly plays like a retro teen mall-flick fantasy in the spirit of “The Lost Boys” or “Gremlins.” One of the more amusing promotions in the history of exploitation cinema was for Jess Franco’s sexy-arty 1967 “Necronomicon.” In the U.S., it was released as “Succubus,” but the distributor claimed that title was too shocking for publication, so newspaper ads included a phone number that could be called to hear the lascivious-sounding word (and its definition).