Super Smash Bros. BrawlEdit
There are items in this game called Assist Trophies, which summon an NPC to appear and help the character. One assist trophy is of a Nintendog, specifically a Labrador Retriever. The Nintendog comes up and licks the screen, causing him to block the view for opponents and, strangely, the character who summoned him.
Super Smash Bros. for Nintendo 3DS/Wii UEdit
On the 3DS version there is a whole stage dedicated to Nintendogs, called the "Living Room". It consists of the Country Home with the Retro Tube TV and Wicker Dog Bed by the front door. The players are the size of toys and are fighting near by some building blocks and the Soft Cube toy. In the background, a Beagle can be seen playing around and watching the fight. In the Developer Direct, one can hear that when playing on this stage, it plays the music when your puppy takes a Bath.
Yet again, the Nintendog Assist Trophy appears. This time, it is a French Bulldog. Other than breed, there appears to be no differences from the last game.