The Grand boasts perhaps the largest ensemble of comic actors this side of The Aristocrats — but instead of performing clever new riffs on an old joke, here they’re straining to apply a well-worn concept (the mockumentary) to a current trend: televised big-stakes poker.

But then The Grand is ultimately less beholden to the Spinal Tap/Guffman gold standard than to the Farrelly Brothers’ Kingpin, recruiting Woody Harrelson to play another once-promising gamer who’s hit the skids — though, this time his alcoholic bowler character is recast as a coke-head card shark who lost his inherited Vegas casino empire through a cavalcade of benders, broads and bad business deals. His return to glory will come at a poker tourney called The Grand, whose $10 million purse will help him reclaim the casino from an unsympathetic real-estate magnate (Michael McKean, who should know better than to latch himself to a second-rate version of the mock docs he helped pioneer).

Harrelson’s competition likewise features talented actors reduced to type: a brother-and-sister team played by David Cross (the smart-ass trash-talker) and Curb Your Enthusiam’s Cheryl Hines (as the eye-rolling wife of a neurotic nebbish, played by Ray Romano); Mad About You’s Richard Kind as a nerdy online poker enthusiast who’s fluked his way to the big table; the reliably brusque Dennis Farina as the Rat Pack–era geezer; SNL’s Chris Parnell as a Rain Man–like number-­crunching savant; and Werner Herzog as a black leathered, rabbit-stroking brute known only as The German (a casting choice that basically amounts to the film’s best joke).

Penn is relying on his stars to improv their way through the disjointed, tangential storyline, but none of his charges bring their A-game. With the cast padded out by cameos (Jason Alexander, Hank Azaria), The Grand crowds the screen with so many one-note characters that you never really care about any one — setting up a big-game showdown with no one to root for. And whatever tension is established in the final rounds (with the actors supposedly playing a real game toward an unscripted outcome) is undermined by a dramatic subplot involving the siblings’ dysfunctional relationship their meddlesome father (Gabe Kaplan, out of retirement for this?) — an ill-advised late-game turn for the serious in a comedy that ain’t all that funny to begin with.