This stage is fairly basic. It is a 3 floor building with 6 apartments. When a player or active item (like a thrown X-Bomb) enters a room, it is revealed. Each room doesn't have any hazards but a Mii in a certain style of room appears in the background doing various activities. Players can also go on the roof but it is easy to get KO'd from the top of the screen.
The Omega version is simply the roof without the ability to go down into the building.
The Island from Tomodachi Life is viewable in the background.
The Miis are taken from the ones on your system. If there isn't enough Miis, the game generates them randomly.
The rooms are not associated with a particular Mii and are random each time it's played on.