Mugman is one of the two idiots who gambled with the devil, and lost. Another hint of him being stupid is when he gambled with the devil, and losing in the process (im actually serious why would anyone do that). He even says himself that he believes that Cuphead is smarter than him. The fact that he is slightly dumb could be hinted that at one point while Cuphead was trying to kill Bendy, he was playing Go Fish! (a card game) with Boris, instead of trying to attack/kill him. It is also said that he and Cuphead are both very stupid, but the comics say otherwise. His canon age is 20, making him the younger brother of Cuphead. He can shoot lasers out of out of his fingers/hands (like in the game cuphead, his character's inspiration), and has a serious gambling problem/addiction, getting him in trouble with the devil himself.
Mugman is one of the antagonists of batqftim, though in a sense it is against his will.