Mushroom Kingdom (stage)
From the Super Mario Wiki
Mushroom Kingdom is the name of two different stages in the Super Smash Bros. series. In the original Super Smash Bros., it is the only unlockable stage. It is set to resemble Super Mario Bros., with brick blocks, falling platforms, Warp Pipes with Piranha Plants, POW Blocks and a scene from the original game in the background. It is unlocked by beating 1-P Mode with all of the eight default players, and then playing all of the other stages in Vs Mode. By going through a Warp Pipe, the player is placed at random at either the other Warp Pipe of the stage or above the abyss. The stage is also based on Super Mario Bros.: The Lost Levels, as there are red Piranha Plants that were first seen in that game, not Super Mario Bros.
The stage returns in Super Smash Bros. Melee, but not as a past stage. Instead, the stage appears much differently from its original design. Various items were added, such as Brick Blocks and ? Blocks, and some were removed, like POW blocks, and floating unbreakable blocks. However, as homage to the old stage, warp pipes in the ditches were added, but have no use. The stage is also a default stage, and is usually where Mario or Luigi are fought. The stage has two holes in the middle of it which, although small, can be very deadly once trapped in one of them. There is also a group of breakable Brick Blocks that cover the entire middle platform, as well as item-containing ? Blocks.
Mushroom Kingdom also appears in Adventure Mode, as Stage 1: Mushroom Kingdom. In this stage, the player must traverse a traditional Super Mario Bros. side-scrolling level. Goombas, Koopa Troopas, and Koopa Paratroopas act as enemies. Half-way through the stage, the player will have to battle a herd of Yoshis. These Yoshis are weaker than the normal Yoshi, so it is easy to knock them out. Once finished, the player continues to the finish line and onto the second half of stage 1, Princess Peach's Castle.
The stage is not included in Super Smash Bros. Brawl. However, a similar stage, Mushroomy Kingdom, is included, with a more modern appearance and following the original appearance more closely, as it is a side-scrolling reproduction of World 1-1 (and 1-2 as well), whose screen does not appear cluttered with the many elements which could be seen in the whole game itself.