In Mario's Madness, Horror Mario was an expert in the video game market and partnered with Dearest in the 90s. When Dearest made a lot of money, he betrayed Horror Mario and locked him in a Super Mario Bros. cartridge. After 30 years trapped, Horror Mario discovered the Dearest's family, especially his daughter and son-in-law, and he went to get revenge on Dearest through them by locking them in his world of madness. He is the opponent of the song It's-A-Me and Starman Slaughter, and is the first and last opponent in All-Stars.