"Good gosh, Cuphead, no!"
—Mugman, begging Cuphead not to accept The Devil's deal, Introduction
Mugman is the deuteragonist of Cuphead. He is Cuphead's brother, and, like the rest of his family, lives on Inkwell Isle. He is played by the second player and can join or leave the game at any time. Due to his deuteragonistic role, Mugman formerly could not be controlled by the first player. However, as of the update in April 2019, the first player can choose to play as him instead.
Mugman is very similar in overall appearance to his twin brother Cuphead, with his head reminiscing a mug, wearing a black, long-sleeved shirt, white gloves, cyan shorts, and brown boots.
What's different about Mugman's appearance compared to his brother is having a cyan color scheme to replace Cuphead's red, a shorter straw, and a much bigger nose. His eyes are smaller than that of his brother. His head is also slightly thinner compared to that of his red brother.
If the player chooses "Yes" in the Devil's cutscene - triggering the bad ending - Mugman's nose, pants and the stripes on his straw turn a darker shade of blue, his handle is broken, and he gains red eyes and sharp teeth, like his brother Cuphead. He also has fire coming out of his head in artworks.
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. This is shown when he begs Cuphead to not make the deal with The Devil, as that would end up costing them their souls in the introduction. (Cuphead went ahead anyway and the brothers were forced to work with The Devil for a bit as a result.)
In Inkwell Isle, Mugman lived a joyful and easygoing life alongside his brother, Cuphead. One day, the boys wandered far from home and ended up in the Devil's Casino despite the warnings of their caretaker, the Elder Kettle.
In the casino, Mugman and Cuphead worked together to gain a winning streak at the Craps table that surprised even King Dice himself. When the Devil approached, he offered the duo a bet: If the boys won, they get all the loot in the casino, but if they lose, the Devil will take their souls.
Mugman tried to stop his brother from rolling the dice, as he knew that gambling with The Devil wasn't a good idea. Unfortunately, his attempts were futile, as Cuphead had taken the bet and lost. The duo begged for The Devil to spare their lives, and was thus sent on a mission to collect his debtors' soul contracts by tomorrow at midnight in order to keep their own souls. Cuphead and Mugman fearfully ran back home to the Elder Kettle, who gave them a potion that gave them powerful abilities and told them to go along with what The Devil says for now.
After doing the tutorial, Cuphead and Mugman proceed to collect the soul contracts, battling bosses, playing through levels, and saving the Legendary Chalice. When they travel from Inkwell Isle One to Inkwell Isle Two, the Elder Kettle tells the boys that their strength is growing thanks to those soul contracts, and soon it will be enough to defeat King Dice in the battle and even the Devil.
Eventually, with all of the soul contracts in their possession, the boys run into King Dice, who is determined to kill them due to losing a bet. After King Dice is defeated, Cuphead and Mugman then meet up with the Devil, who was awaiting them in his office. What the pair does next depends on the choice that the players decide. If they give the Devil the soul contracts, Cuphead and Mugman become his personal lackeys and are turned into demonic cups, creating the "bad" ending. If they do not give him the soul contracts, the Devil will be outraged and battle them.
When the Devil is defeated, the boys accept his surrender and burn all of the soul contracts, releasing the residents from their eternal servitude to the Devil. The boys then went home and told the residents that they are now free from their debt. They are praised for their bravery and an all-day celebration was thrown as thanks. The boys promised to never get into trouble again and succeeded until the next time.
- In the beginning moments of a boss battle, Mugman will extend his straw and take a drink from the liquid in his head. After the update, he may sometimes extend his limbs and look around him.
- Like Cuphead, in the final boss (or failing the Mausoleum level) Mugman will quickly hop from foot to foot, waving his arms with a scared expression.
- According to an interview with Studio MDHR, the liquid inside Mugman's head is the essence of his soul.
- However, people believe that Mugman drinking himself is evidence that the cups hold vodka and/or beer in their heads.
- Just like how Cuphead seems to be based on Mickey Mouse except that Mickey Mouse's shorts are overalls and have the waist going up to the chest and having buttons and suspenders sometimes, Mugman seems to be based on Oswald the Lucky Rabbit, sharing a similar color scheme and being the brother of the protagonist.
- Mugman and Cuphead's animations (when they use the blue potion) may be a reference to when Popeye eats spinach.
- His name may be a reference to the video game character Mega Man, as the pronunciation of his name and as his color scheme is similar to Mega Man's. This is even further supported by the "Run N' Gun" stages, which was the base of Mega Man.
- According to Evan Skolnick, Mugman is an adolescent. However, in a Twitter response to a fan, the Studio MDHR describe Mugman as a "kidult".
- When you remove Mugman (Player 2) from the screen, his head disappears, and he turns into a headless skeleton, but then the bones turn into a pile of ash.