An uncanny mimic and quick-change improviser, Jonathan Winters is one of those great performers who sweep you along in a flow of natural lunacy, whether by diving into his characters or dropping understated asides. The big-kid-bulky Dayton-born comedian gets some welcome playtime in Jim Pasternak’s patchwork tribute, but not nearly enough. Billed as a “comedy/mockumentary,” it assembles improvisations and bits staged with famous fans into a yarn about Winters’s attempts to get his paintings into the Museum of Modern Art. The result is (like much such improv) wildly uneven, reliant on flashes of Winters weirdness and the novelty of seeing Jim Carrey dumbstruck, or the Arquette clan engaged in a mock séance and pep talk. (They’re convened when our hero “loses” his sense of humor, so vital to his Mirò-with-a-punchline painting—which gives an idea of the plotting.) Howie Mandel holds his own, crammed in a cart for a supermarket ramble, and there’s a kick to hearing Winters casually mention his friend Robin Williams’s thefts from his routines. But you might be better off marathon-watching Winters—whose monologue style is already filmic in its quick cuts among bits—playing fanciful raconteur on Johnny Carson.