Old Woman with Masks
Ensor was one of the most influential artists of the 19th and 20th centuries. Though he began experimenting artistically with Realism and Post-Impressionism, he quickly moved on to vast and strange Expressionist pieces, often involving masks and macabre symbols, which are his most lasting works. It's easy to see how the latter movements of Expressionism, especially New Objectivity, and Surrealism benefited widely from Ensor's creativity. But in all of that strangeness that pervaded Ensor's works, there are often present notes of humor, which I think make his pieces so much the weirder and more wonderful.
Skeletons Trying to Warm Themselves
Fall of the Rebellious Angels
Portrait of the Artist's Father
The Bad Doctors