Announced at E3 2001, Pokémon Stadium (ポケモンスタジアム, Pokémon Stadium), is a stage debuting in Super Smash Bros. Melee and returning in Super Smash Bros. Brawl. It is commonly referred to as Pokémon Stadium 1 to avoid confusion with its similar successor, Pokémon Stadium 2.
The basic stage is symmetrical and consists of one large main platform at the bottom and two smaller overhanging soft ones. However, after a varying period of time the basic stage transforms into one of four random variations, turning back to the basic version after a while. The same variation can appear twice in a row, with the basic version always in between. In all variation, under the main platform there is an impassable pillar.
On the background there is a large screen which can display the battle itself, a symbol representing the upcoming variation during a stage transition, or the current standings of players and the time remaining in the match.
The Grass variation takes place in some kind of forest or park. The main platform has slightly elevated plateaus on both sides. A small stream separates the left plateau and the central area, causing a slight depression. A wooden structure with two platforms, one above the other, occupies the middle-left part of the stage, while in the right part there is a tree whose branches form a third platform.
The Water variation takes place near a pond or lake. The whole right side is occupied by a flat pond, while on the left there is a small elevated pier which slopes down on both its sides. Over the pond, two soft platforms are suspended by water spouts, the right one higher than the left one.
On the left side there is a windmill: its arms spin slowly and can be stood upon, but players on the current lowest arm fall. The arms are soft in Melee but hard in Brawl.
The Fire variation takes place in a burning forest. The center of the main platform is occupied by a small depression. On the left side there is a ruined tree: players can stand on top of it, but, due to its height, often need double jumping to reach its top. From the left side of the tree stems a branch which supports a soft floating platform.
On the right side there is a burning shack, the roof of whose porch acts as another soft platform. Note that the fire in the background is purely aesthetical and has no gameplay effect.
The Rock variation takes place in a canyon near a mine. Its terrain is the most uneven of all versions. The right part is flat and empty, while in the middle there are three soft platforms one above the other, of which the bottom one touches the ground and can be walked up from it.
The left side is occupied by a large solid mountain, on whose right side stem two more soft platforms. The walls it creates can cause infinites and caves of life. The top of the mountain itself acts as a solid platform. The mountain's left side is almost vertical and ends almost at the right edge of the stage, leaving however a small walkable space.
Pokémon Stadium was one of the few stages that people in tournaments have almost never questioned being legal, and for a long time, was a starter. Many people considered Pokémon Stadium to be one of the fairest stages in Melee because the shifting terrain was generally not very disruptive to gameplay, and for some time, was thought to prevent excessive projectile camping. However, it was found that Fox and Falco had a large advantage on this stage because the geometry of the stage and terrain allowed them to projectile camp with Blaster very safely. The large horizontal size of the stage benefits their movement greatly, while hindering other characters who cannot traverse across the stage as easily, while the low ceiling allows even earlier KOs for Fox's two main finishers. The transformations also benefit Falco, and especially Fox, greatly in several matchups by either giving them more room to approach or safe spots to camp in. As such, it has been deemed a counterpick stage in more recent rulesets, with some Melee players arguing that it should even be banned because the advantages given to those two characters are far too overwhelming for the majority of the cast.
The stage is more debatable in its neutrality; while it's a starter in the Unity Ruleset and always in seven stage starter lists, Lylat Cruise is often chosen over it in five stage starter lists, while never being a starter in three stage starter lists. The change in unquestioned neutrality comes from changes to the stage itself: the lips at the edge are much more thin and deceptive, occasionally flustering recoveries from slightly underneath the stage or even regular recoveries away from the stage. The most notable change in the stage, however, comes from the redesigned water transformation: while it looks almost the same as in Melee, the blades of the windmill are no longer soft platforms and cannot be passed through in any direction, resulting in stage traversal difficulties and significant caves of life. Brawl players also tend to camp out the Rock and Fire transformations, hiding behind the large rock and the tree until the transformation has ended.
While the stage is not specifically based on anything from the Pokémon video game series, it may be a general representation of a Gym. A possible specific origin could be the Pokémon Stadium games, whose arenas feature a Poké Ball logo in the middle, a crowd watching the battle and, in the case of Gym Leader battles, type-related aesthetics. However, the arenas in the Pokémon Stadium games do not affect the battles in any way.
Another possible source is the Pokémon anime, in which, during tournament battles, the stage changes its terrain frequently to hinder or help either Pokémon. This was seen at least in the preliminary rounds of the Indigo League, in which each of Ash Ketchum's four initial battles was in a different battlefield representing a specific elemental type.
Trainers come from far and wide to congregate at Pokémon Stadiums, the ultimate venues to show off their Pokémon teams. There are many different arenas with varying terrain designs, some of which afford advantages to certain Pokémon. This particular stadium is reserved for huge events and boasts a big screen and spectacular fireworks.