This show hasn’t started yet. Except it has. Before a single acrobat thumbs an airborne nose at the conventions of gravity—this is Cirque du Soleil’s Mystère, after all—there’s merriment afoot. Literally.

Sprinting around the cavernous theater—at age 84—darting between aisles, dumping popcorn on heads, escorting newcomers to the wrong seats, tossing patrons out of assigned seats—is a shambling, impish troublemaker. Wearing a messy mop of comb-proof gray hair, his petite frame lost in a blousy black suit, his ensemble completed by sneakers, Brian LePetit—his clown surname; real name: Dewhurst—is the comic engine revving up Cirque’s longest-running Vegas production.

“I’m the person who disrupts the show,” Dewhurst says. “When the character was being formed, one of the creators said it’s like the old uncle who’s wandered in from a wedding in the other part of the casino and he’s had a few drinks too many.”

Once past his hilarious prelude, Mystère launches … with more comedy via a super-sized baby character, in big bonnet and diaper, who kicks a bouncy ball toward the audience while giggling in high-pitched gibberish, eventually sending it toward a male audience member he exultantly dubs “Papa!” (Now the poor chap is tagged for the duration, his participation climaxing later when, put into the identical infantile outfit, he rides across the stage in a golf cart, his wacky faux-offspring at the wheel.)

Now scoot to the edge of your chair and stay there as an international cast of 75 acrobats, gymnasts, aerialists and dancers in fairy-tale costumes, performing on imaginative sets, creates a surreal Cirque-verse brimming with acts of derring-do.

Fanciful creatures—Red Bird, Black Widow, Birds of Prey, The Double Faces and La Belle, not to mention Spermatos and Spermatites (aka the “seeds of life”)—populate the proceedings. Appreciate the kaleidoscopic tableau they form, plopping you inside a color-splashed dreamscape—one with a throbbing beat, courtesy of taiko drums, including a half-ton behemoth.

Exercise your neck muscles watching a bizarre bazaar of stylized stunts before and above you: the fellow elastically gyrating through a metal cube lit by rainbow flashes; the sky-high guy twisting and spinning on a strip of fabric seemingly stretching into infinity; acrobats leaping off teeter boards into three-deep landings; muscled daredevils balancing each other with handstands; gymnasts scampering upside down on poles, jolting your nervous system.

Set your eyeballs on yo-yo mode to witness bungee-jumping ladies careening like sparkling human rubber bands in a constellation of 2,500-plus colored sequins. Then trapeze artists challenge you to resist vertigo with flip-and-fly exertions. And a fantastical finale brings forth Alice—a, 2,000-pound snail float/creature.

Dropping in between acrobatics is Dewhurst, dispensing shtick such as luring a male audience member onstage, locking him in a box and cozying up to his significant other in the crowd in a riotous routine replete with drinks and candlelight. So what if he’s 84? He’s still a randy rascal.

“If you’re doing something you enjoy and you’re able to do it, why retire?” says the former wire walker. “And it still surprises me when I come offstage and see people who’ve really enjoyed what we’ve created. How lucky can you be?”

When he’s done, you’re even lucky to pluck the popcorn out of your hair.

Treasure Island, 7 & 9:30 p.m. Sat.-Wed., $69-$125 plus tax and fee. 702.894.7722