Flat Zone

From the Super Mario Wiki

Zelda and Fox fighting in the Flat Zone.

Flat Zone is an unlockable stage in Super Smash Bros. Melee. The place is located in Super Flat World, and is Mr. Game & Watch's home stage. It is designed to look like a Game & Watch system, except that it has the Super Smash Bros. logo. Its main gimmick is a figure hanging on the platforms, who will move occasionally, causing some parts of the platform to move somewhere else. Other less common features are falling wrenches, buckets, and other tools. Although that doesn't sound too bad, these are incredibly devastating to even heavy characters. A man carrying oil will pass by and drop it onto the Stage, making that ground very slippery.

The stage is based on Helmet, Oil Panic and Manhole.

It is unlocked by beating Classic or Adventure as Mr. Game & Watch at least once. The music is actually modernized 8-Bit music.

A similar Flat Zone screen appears in Mr. Game & Watch's Target Test stage. Super Smash Bros. Brawl features an enhanced remake of the stage known as Flat Zone 2. The music from this stage is one of the tracks that plays on the stage in My Music.