MADtv has always played second fiddle to Saturday Night Live, but many of its characters–the man-child Stuart and the disgruntled Lorraine, for instance–have been among the funniest on television. Tonight 13 of the writers and cast members perform on a double bill. The first part is “MADtv Writers on Hiatus,” now in its fourth year at the Chicago Improv Festival; it showcases banned and undeveloped TV sketches (some of which have later made it onto the show) performed by writers Tami Sagher, Stephen Cragg, and Jim Wise and cast members Arden Myrin and Crista Flanagan. In the past the material has been risky and unpredictable, and the writers–all stage veterans–have exuded a “so can we” energy. In the second half, called simply “MADtv,” performers Michael McDonald (Stuart), Mo Collins (Lorraine), Ike Barinholtz, and seven other cast members improvise a “midform collage.” IO/Second City alums here include Sagher, Barinholtz, and recent MADtv addition Frank Caeti. Sat 4/29, 7:30 PM, Athenaeum Theatre, main stage, 2936 N. Southport, 312-902-1500, $30.