This underappreciated New York School painter, who died in 1958 at the age of thirty-six, trained with Hans Hofmann (both artists emigrated from Germany), and his early works channel his teacher’s preoccupation with color into syncopated, all-over mosaics of solid squares. Müller began integrating figures into his compositions tentatively, as white skeletons against his usual mosaic background, then in the form of ten buck-toothed witches painted on a totem of six stacked wood panels. That work has a companion in Müller’s ghoulish tableau of Faust’s Walpurgisnacht, which is the anchor for the postwar exhibition “Soldier, Spectre, Shaman,” up now at MOMA. Through March 12.