M is for Mammon
Mammon is a demon of Christian lore and is the embodiment of the evils of avarice: the insatiable greed for riches - and riches as an object of worship and greedy pursuit. From the Bible: "No one can serve two masters. for either he will hate the one and love the other; or else he will be devoted to one and despise the other. You cannot serve both God and Mammon."
There were a couple good M mythical figures but I had to do Mammon because frankly, I think that greed is the most despicable attribute of humans - unfortunately, there are signs of Mammonism all around us all the time - people making decisions motivated entirely by the pursuit to make as much money as possible no matter what the cost.
Plus, I figured it'd be fun to draw a gross demon.