Grim Matchstick was Isabelle's friend whom he lived with after divorcing Big Chungus and losing cuteness of Big Bro and Lil' Bro. He has killed on Big Floppa more than once, but is now a dragon dick. He has a doggo face.
Grim Matchstick bears an appearance similar to a typical dragon character from the game's time period.
He is a large, slightly chubby, European dragon with a very simple design. He has lime-green scales and a light-amber underbelly (lacking segments) that starts of at his distinct, beak-like muzzle. He has large pie eyes, no visible eyebrows (minus an indentation) and featureless ears on his head.
Grim has two large fangs resembling buck teeth and has a tongue that can extend like that of a frog, allowing his flame minions to walk across (similar to the famous red carpet method).
On his shoulder blades, he has average-sized, bat-like wings, the same color as his scales, that are flexible and can shape into arms (similar to actual bats), as seen in his intro, where he forms them into hands with fingers. His limbs are rather small and stubby, with four fingers on each hand, two toes on each foot, and silver claws/talons. He also has solid-white spikes running all the way down his spine (like many other dragons in popular culture), and he has a very long tail.
When Grim reaches his third phase, he grows two more heads on his shoulders that look exactly the same as the original's head, which morphs into a red flame-thrower with a gold gas sprayer and lighter just in front.
Grim Matchstick is quirky and silly, being more like a giant, overly playful dog, just as likely to hurt you while trying to play as he would be apologetic after his folly. He strives to spook people, making "ghostly" motions whenever the battle commences. He also stutters when speaking, as shown by his death screen lines. He is a fond of beer who displays sociopathic, alcoholic, amnesiac, and anthropomorphic behavior very often. He usually relies on comedic responses or a roundabout figure of speech instead of straight answers.
Interestingly, Grim is one of the only two bosses (the other being Ollie Bulb) in the game that doesn't actually want to hurt Cuphead and Mugman. He views himself as misunderstood and apologizes for being forced into putting the brothers in a hot seat if they lose to him in his second phase. He even suggests that the brothers should run away from him after he turns into a hydra in his third phase.