After moving to Florida, Mumma's daughter encouraged him to take an art class, to help take his mind off of his illnesses. The teacher told Mumma his style was "sloppy", and although Mumma never took another class, he continued to paint. Mumma used bright colors, often painting on both sides of plywood or masonite board to produce paintings that primarily consists of abstract versions of portraits focusing on faces and hands, although sometimes he depicted sailboats or animals. His portraits almost always depicted the same close-up, expressionless round face.
Mumma rarely sold his work, and kept his entire collection, between 600-800 works, at his house. After his death, all of his work was acquired by Josh Feldstein. Feldstein promoted his work, published a book on Mr. Eddy, and donated much of his work to major museums throughout the U.S.
