From the Super Mario Wiki
Mario's castle (or Mario Castle) appears in Super Mario Land 2: 6 Golden Coins. Wario steals the castle and transforms it into a level. According to Nintendo Power, he renamed it “Wario Castle.”
Inside are metal spiked balls named Furizō, Fire Pakkun Zō footholds which spit fireballs, and traps shaped like Wario's gloves known as Genkottsu that try to crush Mario. Extremely odd creatures live here such as Floating Faces: a type of bouncing ball with Wario's face on it. If Mario beats Wario, the spell is broken, the castle turns white instead of black, and its "M", turned upside down to resemble a "W", is moved back into its correct position.
Names in other languages