Marbas has the task of dispersing disease among humans. Summoners refer to him as a mighty lion. I can assure you that he is far from it.
He is holding 5 demonic censers, filled with miasma. He zealously scatters pestilence, cholera, leprosy, syphilis and raging madness. Of all the demons, he is the most routed by mankind, increasingly healing the diseases he spreads.
Madness remains its most valuable asset in our corruption, however. The paradox goes even further, because he teaches the mechanical arts, so somehow, by helping us in mechanization, he himself causes his downfall.