From the Super Mario Wiki
Ads keep the MarioWiki independent and free :)
Gamer (stylised as GAMER in the PAL version) is a stage that appears in Super Smash Bros. for Wii U. This stage is based on the stage of the same name from Game & Wario, and it takes place in 9-Volt's room at night.
Like in the original game, 5-Volt appears in this stage, watching over fighters. Her line of sight is indicated by flashes of light emitted from her eyes. If fighters get in her line of sight, they will take great damage and, if their percentage is high, will be blasted off of the stage. Just like in the original game, she can appear in the window, from the bedroom door, and in the TV. If the stage has a sketchbook on it, she can also appear on one of the pages. And if there is a Balloon Fighter game system on the desk, she sometimes appear on the small screen before she gets enlarged. Players can hide inside a pile of book to avoid themselves from being spotted. Occasionally an old man and a cat appear in the room, with the former opening up the window and the latter opening up the door; otherwise they will not do anything. The formation of the stage changes every time players enter the stage.
For the Omega form of the stage, 5-Volt will appear outside but will not open the window, door, or through the TV.
Songs in My Music