Horror franchises are like the monsters who populate them: Just when you think a horror series is dead, it'll rise from the grave in some new, grotesque-yet-unintentionally-ridiculous form.
Yes, like a serial killer who's been buried underground for years, most horror sequels stink to high hell. Mostly because they fall back on the same gimmicks to try to squeeze a little more cash out of the franchise. So we wind up seeing movies where...
The Killer Goes "Ghetto"
When horror sequel writers begin running out of ideas, they'll often resort to throwing the antagonist in new, wholly unexpected settings. One particularly crass plot device places the monster in the midst of city-dwelling African Americans, thus fusing the yin and yang of what terrifies white folks.
One problem with this approach is that the writer must first drag the monster out of its element and shoehorn it into the inner city. In Friday the 13th Part VIII: Jason Takes Manhattan (a.k.a. the lowest grossing F13 flick), it took the entire movie to chronicle the Rube Goldberg-esque chain of events that transported Jason from Crystal Lake to New York City. By the time he actually arrived in the Big Apple, the damn movie was basically over.
Similarly, the Children of the Corn franchise only made it to the third movie before throwing out the series' entire premise (demonic children in rural Nebraska killing adults). In Children of the Corn: Urban Harvest, the murderous tykes moved to Chicago and enrolled in an inner city school deserving of a #1 Coolio single.
The Worst Offender:
Leprechaun. We're not suggesting that the Leprechaun films are anything but stupid, but shit, when it comes to overkilling a lousy gimmick, Leprechaun leaves everyone else in the dust.