Pokémon Change is one of two moves that all three of the Trainer's Pokémon share, the other being their Final Smash, Triple Finish. Performing it changes the Pokémon from Squirtle to Ivysaur to Charizard in that order. However, only one Pokémon needs be knocked out to score against Pokémon Trainer, and the next Pokémon in line will be called out on the revival platform.
While the phrase "Pokémon Change" itself is not an official term in the Pokémon universe, it describes the act of switching out a Pokémon mid-battle. It is a crucial tactic in the games, both in-game and competitively, and takes place before all other actions for that turn (with the sole exception of the move Pursuit, which is designed to counter switching). In the games, as switching takes up the user's turn, the benefits of switching in a Pokémon to face a target it is effective against must be weighed against the risks of being hit hard, setup on, or simply out-predicted by the opponent.
In the Pokémon games, switching out a Pokémon cures minor status effects and all temporary stat modifications, but major status effects (such as paralysis and sleep) will remain unchanged, and HP is tracked individually for each Pokémon. This can be compared and contrasted to Brawl, where the whole Pokémon team share the same damage, but a switched-out Pokémon regains stamina and has almost all status effects removed.
The concept of stamina as Brawl uses it does not exist in the Pokémon games. There is no mechanic that naturally makes a Pokémon less effective the longer it remains in play, unless one counts the fact that moves have limited uses and a single Pokémon used too long will eventually be unable to do anything. Even then however, these limited uses do not replenish while the Pokémon is switched out.
If one Pokémon is KO'd, Pokémon Trainer will summon the next Pokémon in the rotation to the revival platform. Pokémon Change cannot be used again until the starting invincibility has worn off. Pokémon Change also cannot be used in midair.
While changing, there is a little time in which the Pokémon have invincibility frames. Thus the switching animation, which takes some time, can be used to "dodge" various attacks, most notably certain Final Smashes.
Notably, using Pokémon Change ends nearly all status effects on the Pokémon, both positive and negative. This includes super or mini size, Starman invincibility, metal form, Franklin Badges, Screw Attacks, etc. The exceptions to this rule are slowed-time, healing in progress, and Smash Ball readiness, all of which remain through the change. Any held item is immediately dropped.
Like Zelda's Transform, the next Pokémon to appear must be loaded from the disc before the switch can be completed. Pausing can shorten the in-game switch time (since the game loads during the pause), as can lag when online. If the switch time is artificially shortened as such, replays will temporarily freeze at the point the switch is made (since it must take the full time to load). Forcing the game to load the next character through an SD card via hacking will result in a near-instant switch time.
Stamina is a measure of how much energy the Pokémon Trainer's Pokémon have in Brawl.
At the start of a match, each Pokémon has 100 points of stamina. When a Pokémon is in battle, its stamina drops by half a point every second, resulting in 3 minutes and 20 seconds of stamina. Pokémon also lose half a point for every attack they attempt. Once a Pokémon's stamina drops below 40, its standing animation changes to look fatigued, and its attack damage is multiplied by 0.7 + (0.3 × Stamina ÷ 100), with a corresponding reduction in knockback. Thus the attack damage multiplier ranges from 0.779 to 0.7 as stamina decreases. Pokémon regain 0.8 points of stamina per second when not being used, requiring 2 minutes and 5 seconds to fully replenish. When a Pokémon is KO'ed, its stamina is set to 100 − (0.3 × (100 − previous stamina)), so it will be 70% closer to full. This has no effect on the other Pokémon.
The stamina mechanic hurts Pokémon Trainer's competitive usage. As a clear attempt to force players to use all of the Pokémon instead of sticking to one for an entire match, Pokémon Trainer mains are forced to learn three different characters, and are penalized for using a single one for too long. This can also cause problems in matchups, where one Pokémon may hard counter a certain opponent, but the player cannot take advantage of this without suffering a significant strength reduction, giving the opponent openings to strike back. This contrasts with other transforming characters, such as Zelda and Sheik, who have no such penalties.
In Brawl's The Subspace Emissary mode and in Ultimate, stamina is removed, allowing exclusive usage of one Pokémon.
A technique known as "zero switching" can be performed on horizontally moving platforms, which allows a Pokémon to switch out while leaving the player free to react immediately after the next Pokémon is switched in. To perform the technique, the player must initiate Pokémon Change while standing on the edge of a platform that is moving out from under them (such as the left edge of the Smashville platform when it is moving right). If done properly, the next Pokémon will appear in the air, leaving the player free to immediately input any aerial action. The zero switch also gives Squirtle and Ivysaur two midair jumps instead of one upon reappearance. Zero switching is commonly used competitively to avoid the high ending lag that results from switching normally (since the move cannot be started in midair, but this technique allows it to at least be ended in midair).
In Super Smash Bros. Ultimate, stamina is absent, allowing the use of one Pokémon without penalty. Pokémon Change can now be performed in mid-air and has a much faster switch time from not being subject to load times. This reduces the risk of switching Pokémon, greatly improving their synergy with one another. It also improves recovery options, as Charizard maintains its extra midair jump, and Ivysaur's Vine Whip no longer causes helplessness should it miss the edge.
However, Pokémon Change now has a cooldown of approximately two seconds. It can be skipped by using another special move, which overrides the Pokémon Trainer's recall animation.
Pokémon Change grants invincibility frames on frame 1-25. This never changes despite the Skill List noting that spamming the move increases vulnerability.