Improvisation in Chicago seems to have entered a Rube Goldberg phase. The greatest creative challenge facing an improviser now has less to do with making something wonderful right away than with developing a wildly convoluted mechanism to contain it. Hence The Big Yellow Bus, which on the night I attended involved (a) a pair of guest emcees who (b) performed a woozy kind of neo-Smothers Brothers act that supplied (c) inspiration for (d) a quartet of women and (e) a quintet of men who eventually combined into (f) a nontet that (g) built on everything that went before–including a bit about (h) a four-and-a-half-year-old girl who orders a margarita–to (i) entertain people. Unwieldy as it was, the machine worked. I laughed a lot, and even when I didn’t, I admired the skill, energy, and generosity of the whole messy tribe onstage. Open run: Sun 8 PM. Playground Theater, 3209 N. Halsted, 773-871-3793. $8.