The tiny villains are a reference to the original 'Ghostbusters.'
In the clip, Paul Rudd, in his new role as Mr. Grooberson, is seen shopping for dessert at the store. As he grabs some ice cream and syrup, he passes by the marshmallow section. He turns back when he hears some rustling in one of the marshmallow bags. It's then that a tiny marshmallow man, harkening back to the giant Stay Puft man who terrorized the streets of New York City in the original film, climbs out of the bag and bites Rudd on the finger.
He's then met with a gang of the tiny marshmallow men, who are running wild in the store, using a grill to get toasty and make their own self-made smores.
"Mini-Pufts are out of the bag! #ghostbustersafterlife," Reitman captioned the clip.
Ghostbusters: Afterlife is set to come out on Nov. 11 and will star Finn Wolfhard, McKenna Grace, and Carrie Coon, as well as original cast members Bill Murray, Dan Aykroyd, Ernie Hudson, Annie Potts, and Sigourney Weaver.