Super Sudden Death or 300% is a Special Melee mode in Super Smash Bros. Melee, a Special Brawl and Special Smash option in Super Smash Bros. Brawl and Super Smash Bros. for Wii U respectively, and appears as it's own, separate mode under Special Smash in Super Smash Bros. Ultimate. They challenge two to four players to a match where each player's damage percentage is automatically set to 300% each stock. This is much like Sudden Death which occurs after a tie in a standard Vs. Mode match, including the Screen Shrink and falling Bob-ombs in Ultimate.
Super Sudden Death radically changes the way the game is played as virtually any attack with knockback scaling can KO the opponent. As such, this mode tends to greatly favor extremely fast characters such as Sonic and characters with powerful projectiles such as Samus. Even Pit's arrows can cause significant knockback in this mode. Conversely, slow, powerful characters such as Ike are at the greatest disadvantage because the advantage they gain through greater knockback from attacks is negated by all attacks having extreme knockback. In Melee" and Brawl, this mode lacks the falling Bob-ombs that fall on the opponents after a certain duration of time.
In Melee, the songs on Mushroom Kingdom and Kingdom II are changed to Mushroom Kingdom (Finale) and Mushroom Kingdom II (Finale), respectively, during this mode (if one does not play the Dr. Mario alternate music), as they are in the regular Sudden Death.
In Brawl, this mode is also used in Co-Op Event 3: Fastest, Shortest, Sudden Death, but it only lasts for ten seconds.
In Ultimate, this mode has unique Special Rules, which allow to toggle the Screen Shrink and falling Bob-ombs.
Although not selectable as a Special Smash option, players can manually set their starting damage to 300% in Super Smash Bros. for Nintendo 3DS. This mode is, however, selectable in Super Smash Bros. for Wii U as a Special Smash option.