Here's what he's done with the dining room wall--he's in the second picture for scale. His medium of choice here is black tempra paint. Unfortunately, the wall was painted in the last year with eggshell/Matte paint (NOT my choice--an error on the part of the repairman). So it's unwashable and will have to be painted again. Not by Benji.
And here's what he's done with the Master Bathroom. Medium: Black Crayola Marker on Matte Eggwhite colored Paint (also unwashable), cabinets, and toilet seat lid.
Here's a detail of the masterpiece. He tells me it's a rocket.