One of the hazards of renting an apartment instead of owning a home is that there’s a chance you’ll move into a building where there’s an ancient troll living in the laundry room. This is common knowledge. Many rental ads on Craigslist now specify whether there is a troll in the laundry room, and savvy renters know not to consider buildings whose troll status is unknown.

If only the family in the movie “Troll” had been so cautious! They are the Potter family, and yes, the husband and son are both named Harry, and yes, the Harry Potter books have trolls in them, so yes, now we know where J.K. Rowling stole her ideas from. I’d say she improved upon them quite a bit, too. Except for book seven, where they go camping for 500 pages. But I digress.

“Troll” begins with the Potters moving in to an old apartment building shared with five other tenants. The others all live alone, but the Potters managed to snag the one unit big enough for a family of four. Unfortunately, moving day for the Potters coincides with the Witches’ Sabbath, which explains why all the potion-supply stores are closed. It also apparently explains why little Wendy Anne Potter (Jenny Beck) is abducted by a troll the minute she wanders into the basement laundry room, although the direct connection between the Witches’ Sabbath and the troll incident is never clearly established. It seems to be something the movie mentioned randomly, in the hopes that filling the story with details would be the same thing as filling it with entertainment.

At any rate, there’s your troll, fully visible from head to toe, in broad daylight, barely five minutes into the movie. The guy who made “Jaws” could learn a thing or two about not keeping the audience waiting!! Having stashed Wendy Anne away somewhere (I assumed he ate her, but no), the troll uses his magic green ring to shapeshift himself into her likeness, whereupon he rejoins the Potters upstairs. Helen of TrollHere I thought that maybe all the troll ever wanted was a family of his own. Poor li’l lonely, ugly fella! It’s not his fault he looks like veteran White House correspondent Helen Thomas!

Now safely living among the Potters, the troll-as-Wendy does his best to act just like a regular human child. For eight or nine seconds, I mean. Then he goes berserk, wolfs down a hideously greasy fast-food burger (“Just eat it, honey! It’s good for you,” says Mom, falsely), and runs out the door into the hallway to set off the fire alarm. This is not customary behavior for Wendy, and I find it unlikely that trolls are fond of setting off fire alarms, either, but I assume the filmmakers know what they’re talking about when it comes to trolls. The movie is called “Troll,” after all.

The fire alarm brings everyone out of their apartments so that the movie can introduce them to us. One of the neighbors is Elaine from “Seinfeld.” Another one is a macho jogger who used to be in the military. Another one is a very old lady named Eunice St. Clair (June Lockhart) who dresses like someone from the 1880s. Another one is Sonny Bono.

Now, it is sometimes said that “Troll” “stars” Sonny Bono, but that’s not true — not just in the sense that nothing could really “star” Sonny Bono, but because he’s only in a few scenes before the troll turns him into a plant. And in those few scenes, he’s depicted as a swaggering, bathrobe-wearing ladies’ man — he describes himself as a “swinger” and behaves in a lurid fashion — so his transition to flora is definitely an improvement.

But I have gotten ahead of myself. Yes, the troll’s plan is to turn each of the building’s apartments into a different part of the fairy world that he once inhabited, possibly in another dimension. (This is among the many things that the movie does not explain very well.) The swinger’s apartment is soon lush with plant life and small fantastical creatures, and the macho jogger’s flat is next to go. It’s easy for the troll to gain access to these places because he’s disguised as a cute, towheaded little girl, and because people let unaccompanied children into their apartments all the time, like the building’s a damn daycare or something.

Wendy’s parents blame her weird behavior on the stress of moving to a new house, but her older brother, Harry Potter (Noah Hathaway), suspects something is wrong, especially after Wendy picks him up and throws him across the room, which no muggle could do. No longer feeling safe at home, Harry Potter befriends Dumbledore — er, Eunice St. Clair, the old lady upstairs, who, like everyone else, lets children wander in and out of her apartment at will. On his second visit, Harry Potter asks, “Eunice, are you a witch?” This comes out of the blue, and only because she has a lot of weird knickknacks. Harry’s threshold for witchdom is very low. But he happens to be right in this case: She is a witch, and she readily admits it, very nonchalantly, as if he’d asked if she likes butterscotch.

Meanwhile, Wendy has met the building’s other tenant, an English professor named Malcolm (Phil Fondacaro), who is a dwarf (the real kind, not the “Lord of the Rings” kind). Wendy calls him “brother elf,” implying that trolls and elves are related, or at least allied in the fairy kingdom; Malcolm, who is a human and doesn’t know Wendy is a troll, and who isn’t an elf at all, humors her and accepts an invitation to dinner at the Potter home. While they’re eating, Wendy asks Malcolm to recite “The Faerie Queene,” the epic poem from the 1590s written by Edmund Spenser. Even though it is the longest poem in the English language, Malcolm has it memorized, and his recitation of it causes the troll-like beings Wendy has created in the other apartments to chant along. Something is happening! The movie won’t tell us what, or why, or how, but something is definitely happening! Then Eunice the witch blows a horn and the chanting stops and Wendy the troll gets a headache, which her parents blame on the stress of moving. Wendy could slaughter a cat and bathe in its blood and her parents would blame it on the stress of moving. This troll was lucky to infiltrate such a dumb family.

Harry Potter, the smart one, thinks he’s got it all figured after watching an old B-movie on TV in which characters are replaced by pod people. (It’s interesting to see what the people who made “Troll” think a bad movie looks like.) Then Eunice explains everything to him: how she became a witch, who the troll is, what it wants, etc. She passes along this information very casually, even though the troll’s plan, if fulfilled, would mean the end of all life as we know it. She also says there’s only a 72-hour window before the troll’s work is complete, so they’d better hurry — but then, even though she’s the one with magic witch powers, she stays home and sends Harry out to deal with it, presumably because it’s noon and her stories are on. (Alternate joke: presumably because it’s after 5 p.m. and she doesn’t like to go out at night.) Only after Harry proves useless in the field of troll-killing does Eunice get off her lazy butt, make herself young again (why didn’t she do that 100 years ago?), and take care of business.

Another one of the many things that “Troll” is unclear about is whether “Troll” is supposed to be scary, funny, or some combination of both. If it’s supposed to be neither, then, well, good job! And if it’s supposed to be really embarrassing, then it’s one of the most successful films I’ve ever seen. It’s also convinced me to avoid my apartment building’s laundry room forevermore, though I might have been looking for an excuse to do that anyway.

(Note: You may have heard of “Troll 2,” which is a very famous bad movie with a large cult following. Despite its title, it has nothing whatsoever to do with this film, and in fact features goblins, not trolls. It is also, in my opinion, not a good candidate for Eric’s Bad Movies. Its awfulness is so self-evident that mocking it would be superfluous. Simply watching it would provide far more laughs than anything I, or anyone else, could write about it. Trust me.)