B

Horror movies are ripe for spoofing, but it’s a hard thing to pull off. “Tucker & Dale Vs. Evil” succeeds far better than most. Though it trails off toward the close, the first half is clever and funny, and the second, though not nearly as strong, still has some chuckles.

The script by Eli Craig and Morgan Jurgenson upends the usual “Texas Chainsaw Massacre” scenario by portraying rustic hayseeds Tucker (Tyler Labine) and Dale (Alan Tudyk) as amiable doofuses who nonetheless terrify the carload of college types they encounter at an out-of-the-way gas station. That’s because the young outsiders have seen entirely too many slasher flicks in which kids like them have fallen victim to the murderous madness of local yokels, and their de facto leader Chad (Jesse Moss) is certain they’re in danger. It doesn’t help that the area is famous for being the place where a maniac offed a bunch of tourists years before.

But it’s all in their minds, of course. Tucker and Dale are just a couple of beer-swilling good ol’ boys on the way to the run-down shack Dale’s bought as a “vacation home.” But when they go fishing and rescue one of the teens (Katrina Bowden) from drowning and take her back to their cabin, the girl’s friends assume she’s been abducted and fear she faces a fate worse than death. So they take it upon themselves to rescue her. Unfortunately, they misconstrue everything they see and in trying to be her saviors most of them manage to kill themselves off instead.

Up to this point the movie is consistently amusing and sometimes hilarious. The writer-directors know their target well, and have concocted amusing riffs on the genre cliches, including some wickedly gross-out death scenes. And Labine and Tudyk create a real two-stooges vibe as the pleasantly dimwitted title duo.

Unfortunately, the plot shifts gears in the final reels, with a twist that essentially reverses roles. It’s a take-off on another of the conventions of horror flicks, but it doesn’t generate nearly as much fun as what’s preceded. The threadbare production is also more evident toward the close—or maybe it’s just more noticeable because your interest is flagging.

But if it doesn’t quite go the distance, “Tucker & Dale Vs. Evil” earns enough laughs along the way that it should be an amusing ride—especially for fans of slasher flicks (or those who have always thought the genre was totally ridiculous).