If Michael C. Hall wants to shed the stiff-in-a-suit image he honed on Six Feet Under, a coke-snorting hornball role should help. ”Let’s play doctor!” he burbles, wagging his butt. ”My prostate hurts!” Hall’s Mr. Marmalade is the pretend pal of a tutu-clad toddler (Mamie Gummer) with an insanely overactive imagination; he’s also the quirky centerpiece of Noah Haidle’s cluttered, colorful black comedy. Haidle overdoes the eccentricity — a suicidal preschooler and talking plants? — but he doesn’t skimp on originality.