It's the glasses. Dark glasses, no less! The medieval iconography of Moses with horns is goofy enough, but these spectacles are irresistible. The question is, What to do with the picture besides use it to expound an oddity in art history? Maybe let it provide a model for some imaginary wizard? I like the idea of substituting a goat's face for the man's.
Incidentally, the Hagenau Bible, from which the picture comes, also illustrates a moment in publishing history, the move into mass-produced books through a rationalized system within scriptoria. Might the head scribe of a magical scriptorium be a demon?