A mixer assembly for treating exhaust with an injected reductant as the exhaust flows through an exhaust gas passageway includes a tubular shell and a rod. A first end and a second opposite end of the rod are fixed to the shell. The rod has a serpentine shape with a plurality of parallel extending portions interconnected by curved portions. The curved portions are positioned proximate an inner surface of the shell such that the rod traverses the exhaust passageway. The mixer assembly is positioned such that the rod is directly impinged by reductant injected into the exhaust gas passageway.