From the Super Mario Wiki
Wario's House first appears as the tenth stage in Mario & Wario, but it returned as a rather minor location in the WarioWare series, where it is shown to be in Diamond City. While it was originally a spacious and somewhat unkempt house, it was redesigned as a smaller home. Wario remodeled it as the headquarters of WarioWare, Inc., although it was restored after the events of the first game and moved from the top of a mountain to lower ground. Wario still controls his company from that location, although he usually just sits in front of the TV. In WarioWare: Twisted! the music box from Wario Land 3 is displayed on Wario's desk while a picture of the Golden Pyramid from Wario Land 4 appears on the wall beside it. In Wario: Master of Disguise, Wario's house can be seen in the intro movie and the main menu screen, where he once again relaxes and watches TV.
Wario's house returns once again in the Wii U party game Game & Wario. The house appears in the opening intro, which shows Wario sitting in his home, watching television before he realizes he needs to make a game.
In Wario Land II and Wario World, is shown Wario residing in his large castle, which he eventually acquired with his treasure-hunting wealth. Wario has been seen spending time in his house in more recent games.
Mario & Wario
Wario's House is the tenth stage found in Mario & Wario. It is continued from Wario no Niwa, although if the player receives a Game Over from this point on (not counting the EXTRA stage) then they will lose all their progress and have to continue their adventure from LEVEL9-1. A stone guardian watches Wanda's invasion of the house. During the stage intro, Wario drops an oil can with a "W" on it.
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