The stage at first is just a completely flat living room, and occasionally blocks and other assorted playthings will drop from above, damaging anyone they hit. Players can now battle on these platforms, but the formation of the platforms will change regularly.
In the background, there will be at least one Nintendog playing, and there are 5 breeds of Nintendogs that may appear. Nintencats will also appear on occasion. 
The stage is based on the main hub of the Nintendogs games, which is also a living room. This room is used for playing with your dog, by, for example, throwing toys at him that function as platforms in the stage.