As the future of Coney Island sits in peril, like a car at the top of the Cyclone, the abundantly gonzo weirdness that has made the one-time resort a repository of tall tales and maverick exploits might appear to be on the wane. Astroland Amusement Park will reopen for one more summer, but after that, the pending redevelopment of the boardwalk and its environs — so awash in the smell of fried batter, the echoes of roller-coaster screams, and the candy-colored vibrancy of the midway — threatens to whitewash one of the last great, real American places.

“American Carny: True Tales from the Circus Sideshow,” a 2005 documentary making its debut on DVD today, is important for celebrating Coney Island as a vestige of a sideshow culture that barely exists anymore. The film is mostly about Todd Robbins, a 49-year-old entertainer who is one of the featured attractions at Sideshows by the Seashore. The charming little theater, tucked under the Coney Island Museum at the corner of Surf Avenue and West 12th Street, hosts the country’s (if not the world’s) only ongoing 10-in-1 circus sideshow. Here, acts such as the Human Blockheads hammer nails into their nasal cavities, and a woman named Insectivora, her face partially decorated with a Maori-style tattoo, eats fire.

Mr. Robbins, who also runs the Coney Island Sideshow School, is a master of many trades: He swallows swords, chews up light bulbs, walks on broken glass, and cheerfully inserts his fingers into a nasty-looking rodent trap with rusty metal teeth. All the while, his decidedly non-freakish demeanor sets up an amusing contrast with his stunning feats, which he narrates as he performs them, offering bits of sideshow history and some corny humor. The vibe, instructional while still maintaining an air of mystery, is enjoyable and inclusive. Kids, please don’t try this at home.

Filmmaker Nick Basile picked an irresistible topic, and even lured America’s no. 1 “carny” fan, the comedian Penn Jillette, to deliver a few opening words to his project. But for all its enthusiasm and colorful characters, “American Carny” is too narrow in its focus and is rarely interested in wandering off the boardwalk. The film often feels like one long, self-congratulatory infomercial for Mr. Robbins — a winning fellow to be sure, but not so compelling as to carry an entire 99-minute documentary.

Mr. Basile spends time with some of the other sideshow favorites and captures a sweet valedictory appearance by sideshow legend Melvin Burkhart (“the original Human Blockhead”), yet the effort feels at once padded out and incomplete. There’s no mention of other, sympathetic performers — such as the Jim Rose Circus, which took sideshow culture to the alt-rock masses on the Lollapalooza tours of the 1990s — or much discussion of carny-dom’s popularity on the New York nightlife circuit, where it happily coincides with a neo-burlesque revival.

The most interesting figure here turns out to be Jennifer Miller, not a bearded lady but a “woman with a beard,” whose presence offers commentary on the role of women in the sideshow and the shifting concept of what it is to be a “freak.” More such critical context would have gone a long way toward making “American Carny” feel substantive, rather than like a mildly entertaining diversion.