|Not to be confused with Kirby's Mom or Papa John.|
The Devil, also known as Satan, is the main antagonist in If Mario was in... Cuphead.
When Mario loses at a casino game, he says that he'd do anything to win, Satan then appears and says if Mario wins the next roll, he’ll win all the loot in his casino, but if he loses, his soul belongs to him. Mario of course loses and sends him to Inkwell Isle. Mario then meets Cuphead and Mugman who souls were going to be taken if they didn’t defeat all the bosses. They spot a portal to hell where Satan appears and says that he need one more soul... Mario’s! They say no because Mario's their friend but Satan then threatens to take Mugman's soul if Cuphead doesn’t kill Mario. Cuphead then almost shoots Mario, but shoots Satan instead, allowing Mario to attack Satan and managing to bring Mario back to the casino.
Satan is later summoned by Magolor in SMG4: If Mario Was In... Kirby Star Allies to attack Kirby and Mario. Though compared to his appearance in Mario Was In Cuphead he looks very different. (This might be his ability to take on several forms, making his physical appearance rather unpredictable.)
He later appears in SMG4: Stupid Mario Maker 2. However, it seems that Mario is now on good terms with him.
He later appears in War of the Fat Italians 2021 where he brings Melony to hell to help her create a super strong password in a challenge to see who can create the most strongest password.