Stamina is a gameplay option that replaces the traditional Super Smash Bros. damage percentage with a "HP gauge" similar to the life bars of conventional fighting games, which must be depleted to defeat characters. Stamina was a Special mode option prior to Super Smash Bros. Ultimate, where it became a standard rule option. Battles with Stamina rules also appear in some event matches, one possible Smash Run Final Battle, and some spirit battles.
In Stamina, every hit to the player depletes some HP from them. Once a character reaches 0 HP, they are KO'd, though characters can still be knocked off the stage through conventional means. However, knockback is not affected by the amount of damage the player has taken. From Melee to SSB4, characters in Stamina only have a single life, but in Ultimate, the mode can be used with stocks; when a character reaches 0 HP, they will be instantly KO'd and respawn for as long as they have stocks remaining. When a character is defeated, the game will temporarily slow down, and the character will let out one of their KO cries, which varies based on the game. If the victim is hit by a very weak attack when they are KO'd (or defeated by a damage-over-time status effect like flower), they will perform a unique animation of them dramatically crumpling to the ground, usually falling backwards or on their knees; otherwise, the victim will simply tumble down onto any solid ground.
Defeated fighters will always stay in their prone position and flash red; they cannot be controlled by the user and will always enter a state of tumbling when hit, and can be knocked off the stage and KO'd with a blast KO as usual. In SSB4 onwards, defeated characters can also be eliminated completely if the victim is trapped in certain hazards such as Danger Zones. Any helper characters, such as Pikmin, will still stay next to the knocked out combatant, with the exception of Luma, who will be KO'd alongside Rosalina, and the partner Ice Climber in Ultimate, who will be KO'd alongside the leader. In Ultimate, defeated fighters will explode after a brief moment, removing them from the battlefield.
Healing items and moves cannot heal a fighter's HP past their starting amount.
Mechanically, characters are considered to have a negative damage percentage while they have positive HP, which is why they take little knockback until KO'd, at which point they begin to take more knockback as damage rises as expected.
Stamina mode was first introduced in Melee as a Special Melee option. Unlike the future games, the HP of every fighter is fixed to 150 HP. There is no legitimate way the player can edit the starting stamina, barring use of an Action Replay to modify flags in the match's data; the instruction booklet, however, shows a screenshot of Stamina Mode with HP higher than 150, suggesting that selectable Hit Points was previously considered.
Melee's version of Stamina is unusual for not having a results screen, as it will send players directly to the character selection screen once a single player remains. This makes it the only mode in all of Melee with such a property; as a result, players can use the name entry glitch to use Master Hand in the mode without causing the game to crash if he wins a match.
Characters who have 0 HP remaining in Melee's Stamina mode will let out their Star KO cry.
Brawl once again offers Stamina mode in the game's Special Smash mode, Special Brawl. Players can now select their starting HP individually via the Handicap option, allowing increments of 10 between 10 HP and 300 HP, as well as only 1 HP. Brawl's 1HP setting allows for lightning-quick games with no legitimate winner if all players also have the flower status on them: all fighters will be KO'd at the same time, forcing the game to select a random winner.
The addition of Final Smashes affect the bodies of fighters KO'd by one: if the victim is trapped in a "trapping" Final Smash such as Ike's Great Aether or Link's Triforce Slash, the character will be "dropped out" from the move once their health is depleted.
Characters who have 0 HP remaining in Brawl's Stamina mode will let out their Star KO cry, with an additional echo effect added to it.
In Super Smash Bros. for 3DS/Wii U
In Super Smash Bros. for Nintendo 3DS, Stamina mode is not a selectable option due to the lack of a Special Smash mode; as a result, there is no way to play with Stamina rules manually. However, Stamina can potentially appear as a random possible Final Battle in Smash Run. This is the only way to play with Stamina rules in for 3DS.
In Super Smash Bros. for Wii U, Stamina returns as a Special Smash option, but the 1 HP option is removed, meaning the HP range is now 10-300HP.
Unlike the other games, characters who have 0 HP remaining in Smash 4's Stamina mode stay completely silent when knocked out, although the slowdown effect still occurs.
In Ultimate, Stamina is now available as a standard rule option which can be combined with Time and Stock modes. As Stamina mode is no longer a part of Special Smash, it is now possible to play Stamina battles with up to eight players. The maximum HP possible has been drastically increased, as players can now have HP ranging from 10-999 HP.
When playing with more than one stock or during a timed match, losing all HP causes an instant KO and respawn; on the fighter's final stock, KO'd characters will enter their motionless defeated pose, and will eventually explode after a few seconds (instead of permanently staying on screen unless knocked off, like in previous games). As with other default modes, the final blow will feature the "Final Zoom" effect regardless of how strong the move was, unless the KO was a Blast KO; if such, the game just ends like a normal match.
In Ultimate, victims caught in a trapping or cinematic (e.g. Chain Attack, Max Malicious Moonsault, The Mighty Jinjonator) Final Smash will not go below 0.1 HP until the final hit. However, a few of these Final Smashes do not have this ability (such as Isabelle's Dream Town Hall or Luigi's Poltergust G-00), and opponents that attack a trapped foe in a non-cutscene Final Smash will still KO the victim before the move ends. Additionally, Final Smashes that previously had extremely high or OHKO potential (such as Critical Hit) have their knockback significantly reduced to prevent them from KOing opponents with high HP, unlike in Brawl or Smash 4.
Characters who are out of HP and lost all of stocks in Ultimate's Stamina mode will let out an echoed version of their primary Blast KO cries. As a result, Samus no longer make any sounds during the animation. There are a few exceptions: Marth and one of Ike's alternate costume (depending on the current language) use their alternate KO voice clips, Mario, Dr. Mario, Hero and Terry use one of their heavy knockback cries, both Joker and Banjo & Kazooie use a unique knockout voice clip, and Mr. Game & Watch, R.O.B., Mega Man, and the Mii Fighters fall silently. As a result, Daisy (who exclaims "Ow, ouch!"), Zelda (who exclaims "いやぁっ!" (Nooo!)), and Zero Suit Samus (who says "No!") are only characters who speak during the animation. Some team characters appear to be inconsistent: the Ice Climbers have both Popo and Nana scream simultaneously; for Pokémon Trainer, the trainer does not vocalize if the match was 1-on-1, or there were no more allies in team battle (as in normal rule); and for Rosalina & Luma and Banjo & Kazooie, only Rosalina and Banjo vocalize during the animation (for Luma's case, they will have the instant KO explosion regardless of how much stocks are left; Kazooie lacks blast KO voice clips altogether). If a character is defeated by hazards that can instantly KO them (such as Danger Zones in The Great Cave Offensive and getting crushed by merging platforms in Midgar), their knockout voice clip will be heard, but the instant KO explosion still occurs even in the last stock, like normal rule.