A Final Smash (最後の切りふだ Saigo no Kiri Fuda, Final Trump Card) is a special attack in Super Smash Bros. Brawl and in Super Smash Bros. 4. Final Smashes are incredibly powerful in comparison to most other attacks, generally leaving the user invincible for the move's duration, are generally unblockable, and, if properly executed, usually have the capacity to KO at least one opponent. Final Smashes performed correctly will give the player a great advantage, and may help to catch up to others or cement a commanding lead. Many Final Smashes also temporarily slow down stage elements, such as platform movements and motions in the background.
To perform a Final Smash, a player must first either destroy a Smash Ball or fall sufficiently far behind that they are given a "Pity Final Smash". Once either of these happen, the player's character will be engulfed in a multi-colored aura; pressing the special move button in this state will trigger the Final Smash. However, if the player's character takes sufficient damage after collecting a Smash Ball and before performing the Final Smash, the Smash Ball will fly out of their character and be returned to play.
Only one Smash Ball or Final Smash can be present on-screen at any given time.
 Prior to Brawl
It was revealed in an interview with Nintendo's president, Satoru Iwata, that Masahiro Sakurai had intended for Final Smashes to be included in the original Super Smash Bros., even going as far as to record voice clips for each of the Final Smashes. The idea, however, was held off until Brawl. While the voice clips cannot be listened to in ordinary gameplay, the debug menu allows the player to listen to various clips that do suggest the idea, such as Ness yelling "PK Starstorm!".
 Pity Final Smash
A Pity Final Smash occurs when a player is KO'd and is 5 points behind the current leader (thereby allowing the player in 2nd place or below to earn one, provided the gap is large enough.) This player respawns with the ability to perform a Final Smash. This Final Smash cannot be dropped by the player. Pity Final Smashes can be disabled only by turning off items completely - simply setting overall item frequency to 'None' does not work.
While Final Smashes tend to be unique among characters, there are certain categories they can be sorted into.
 In competitive play
In tournaments, all items are turned to off and none, including Smash Balls. This means that Final Smashes do not appear in tournaments. While the consensus has been that any randomly appearing factor is detrimental to competitive play, such a decision undoubtably favors certain characters more than others. Some characters, such as Meta Knight, have excellent regular attacks, but have poor Final Smashes, while others (like Link) have poor regular attributes, but have very good Final Smashes. Certain smashers feel that this contributes to the brokenness of certain characters, while removing viable options from others. Despite this complaint, Smash Balls remain disabled at this time along with all other items due to their unpredictability.
Because items are turned to off and none, and tournament rules specify only 3 stock, Pity Final Smashes also do not appear in tournaments. One might argue that allowing Pity Final Smashes would allow a badly beaten player to stage a comeback, as they do not appear at random like Smash Balls do, and any player good enough to push an opponent so far will likely win the match anyway. However, this can only happen in a match of at least 6 stocks, which is generally accepted to be too high for tournaments.