Super Sudden Death and 300% are Special Melee and Special Brawl modes in Super Smash Bros. Melee and Brawl, respectively. They challenge two players to a match where each has a 300% Damage Percentage from the very beginning, as opposed to 0%. This is much like the Sudden Death mode which occurs after a tie in Versus Mode in Melee and Brawl, with the only difference from being that this mode lacks the falling Bob-ombs.
Super Sudden Death radically changes the way the game is played as almost any attack with knockback can kill 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 are at the greatest disadvantage because the advantage they gain through greater knockback from attacks is negated by the fact that all attacks have extreme knockback. However, both players are able to tip the scales either way in their favor. Also, items are prone to being great match enders.
This mode can be played by a player and Computer Player as well, but in Melee the computer tends not to play as if they were at 300%, but instead as if it were a normal game.
Lucario tends to have a greater advantage in Super Sudden Death mode due to its "high risk, high return" property.