By joining forces for the first time, Steppenwolf and Second City have raised expectations for this show, and its two men in pajamas deliver with the stuff of dreams: absurdity displaces logic, characters morph midsentence, humans embody horses and alphabet letters. Writer-performers Shenoah Allen and Mark Chavez, who've worked together since the early 90s, inhabit an eccentric comic world unburdened by the self-congratulatory pop-culture references of most improvisers. Though it's scripted, the show resembles long-form improv. The hybrid format allows Allen and Chavez to hone their exceptional skills at difficult improv techniques--notably the tricks of seamlessly changing scenes and recalling narratives and characters. They merit the theater venue too, bolstering their inventive wit with dazzling displays of mime and vocal dexterity. Through 4/2: Thu-Fri 8 PM, Sat 7 and 9:30 PM, Sun 3 and 7 PM, Steppenwolf Theatre Company, Merle Reskin Garage Theatre, 1624 N. Halsted, 312-335-1650, $15.