What's different about Mugman's appearance compared to his brother is having a blue color scheme to replace Cuphead's red color-scheme, a shorter straw, and a much bigger nose. His eyes are smaller and is head is slightly thinner. Mugman's appearance remains the same, save for a few differences. Like Cuphead, his colors are a bit duller, has yellow gloves all the time, and his skin has a beige tint to it, and his shoes having an orange tint. He also has thin eyebrows.
At night, he wears a blue onesie.
Mugman is fun-loving like Cuphead, though he is shown to be careful and less rash compared to his brother, and acts as the voice of reason for him. While he cares for Cuphead, the two of them bicker half the time. His voice actor Frank Todaro describes him as "the more cautious one, and does love adventure, but usually just tries to make sure Cuphead and him stay alive".
Although being a timid person who shies away from danger, he has displayed incredible feats of courage. He saves Cuphead from damnation by pulling his brother's soul out of the Soul Ball machine and restoring it to his body and has so far defeated the Devil three times. In Sweater Off Dead, while Cuphead is secretly panicking about the Devil taking his soul, Mugman is the one who decides to take decisive action and takes him to Quadratus. During the episode Dangerous Mugman, he became more courageous and confident when he believed wearing Cupman's goggles would magically make him braver, until he proudly realizes he did all the stuff by himself.
He is also very in touch with his feminine side, shown when babysitting Baby Bottle and being excited at it calling him "mama", disguising himself as a bride when going out, and knitting an invisible sweater for Cuphead.
Unlike Cuphead, who loves to be the center of attention, Mugman gets bad stage fright and freezes up in front of an audience.
Cuphead is Mugman's older brother and best friend. Like all brothers, Cuphead and Mugman often bicker over trivial things like ice cream or simply because they're not supposed to. Despite that, Mugman deeply cares for his older brother. The two are opposites, but complementary: While Cuphead is impulsive and acts without thinking about the consequences, Mugman acts as a conscience for him and brings him to his senses, with varying degrees of success. He often gets dragged into dangerous situations because of Cuphead, and while he enjoys adventures too, his concern is that he and his brother get out safely. Mugman never blames Cuphead when he puts their lives in danger, and is always by his side, even if he is sometimes annoyed by his carelessness.
Despite his cowardice, Mugman shows extraordinary bursts of courage whenever Cuphead's life is in danger. In the first episode, he prevents his brother's soul from being stolen by the Devil. In the episode Sweater Off Dead, after Cuphead wakes up from a nightmare, Mugman decides to act and takes him to Quadratus. His brotherly love for Cuphead allows him to knit him an invisible sweater extremely effective against the Devil, and he protects him from all the Devil's attempts to steal his soul. At the end of the episode, when Cuphead thanks him for knitting the sweater, Mugman replies that "he'd nerver make a sweater for no other than his dearest sweet, sweet brother".
Elder Kettle is Mugman's caretaker, along with Cuphead. He shows some annoyance with the rules and chores imposed by his guardian, but not as much as Cuphead. In the first episode, while Cuphead does everything to avoid painting the fence, Mugman, on the other hand, tries to stay focused on his task, until he and his brother are distracted by the Carnevil. In the episode Baby Bottle, he does his best to keep Elder Kettle's radio intact, knowing that he and Cuphead will be grounded if they break it.
Mugman seems to hold Elder Kettle in higher regard than Cuphead. In the episode Root Packed, while he and Cuphead originally wanted to take advantage of Elder Kettle's sleep to go to the movies, Mugman soon feels guilty, and suggests to his brother that they should take care of his vegetables like Elder Kettle took care of them when they were babies, proving that he is grateful to his guardian for raising him and his brother. Afterwards, he does everything he can to protect the vegetables from the Root Pack. In the episode Handle with Care!, he is proud to show his "man handle", not knowing that it was Elder Kettle who glue it back on. In the episode Dirt Nap, when Elder Kettle thought the boys wanted to get rid of him, Cuphead and Mugman immediately clear up the situation, saying that he is their Elder Kettle, and that they love him, before giving him a hug.
The Devil is Mugman's enemy, along with Cuphead, since he tried to steal Cuphead's soul. Initially terrorized by the Devil, Mugman doesn’t hesitate to stand up to him, determined to protect his brother from the evil creature. In the first episode, Mugman prevents his brother's soul from being stolen by the Devil, and after a frantic chase, he manages to trick the Devil into destroying his game Soul Ball game, releasing all the souls trapped inside, and provoking his anger.
In the episode Sweater Off Dead, Mugman knits an invisible sweater extremely effective against the Devil to protect Cuphead, and afterwards, he manages to foil all the traps set by the Devil. In the episode Sweater Luck Next Time, he is just as fed up as Cuphead with the Devil's useless attempts to take his soul. At the end of the episode, he defeats the Devil once again by putting the invisible sweater on him.
Cuphead and Mugman meet Baby Bottle in the episode of the same name, when someone dropped him off at their front door. Mugman becomes instantly attached to the baby, to the point of being overjoyed when the baby calls him "mama." When Cuphead gets angry after Baby Bottle bites him, Mugman prefers to defend the latter, convinced that babies need all love. Even after Baby Bottle drops the goldfish bowl and locks him and Cuphead out, Mugman doesn't change his mind. He finally gets angry when Baby Bottle tries to destroy Elder Kettle's radio, and when the baby rips the head off his teddy bear, he tries to attack him physically, then realizes that he is not a baby but " it's evil." What happens next only confirms it, as he and Cuphead are unable to deal with the baby and its evil intentions. At the end of the episode, Mugman, like Cuphead and Elder Kettle, is relieved to get rid of the baby by leaving it at someone else's door.
Porkrind is a merchant whose store is located not far from the house of Cuphead and Mugman. The two brothers instinctively go to his store whenever they need something, like paint in the first episode, or glue in Handle with Care.
Mugman seems to like Porkrind, which is not reciprocated, as we can see in the episode Dangerous Mugman. Mugman is excited as he tells her a story about a shoe he lost, not knowing that it deeply upsets Porkrind. He is offended when the merchant doesn't believe him capable of accomplishing the mission he and Cuphead have set out on, and he is determined to prove to him that he can be brave too. At the end of the episode, he is grateful to Porkrind for giving him the arcade game, without realizing, once again, that it is just a way for Porkrind to get rid of him and Cuphead.
In the episode Sweater Off Dead, Mugman decides to take Cuphead to see Quadratus after his brother has a nightmare about the Devil. Mugman holds Quadratus in high esteem, saying that he is a great sage who is supposed to know all. When Quadratus orders him to knit an invisible sweater for Cuphead, he obeys without flinching. It is unknown how Mugman learned about Quadratus.
Cuphead and Mugman meet Ms. Chalice in the episode In Charm's Way, and observe her as she manages to get what she wants for free. Both of them are curious about how she does it and follow her to the movies, until she notices their presence. Unlike Cuphead, who wants to look cool in front of her, Mugman prefers to be honest, referring to himself and his brother as a couple of dumb-dumbs, and admitting that they failed to steal the cookies from Elder Kettle. He follows his advice carefully and is pleased to see it pay off (at least, he thinks it does), when the trio manages to get into the cookie factory. Later, in a Season 2 episode Mugman loses his trust on Ms. Chalice after she abandons him and Cuphead to the police, even slamming the door on her after arriving at their cottage, but seems to forgive her later on.
- As seen in the episode "Sweater Off Dead", Mugman is good at knitting, as he was able to knit an invisible sweater for Cuphead with ease.
- Mugman seems to suffer from glossophobia. As seen in the episodes "Roll the Dice" and "Root Packed", he freezes in terror whenever he has to speak in public.