Helpless

There are certain actions that will cause a character to become helpless (sometimes called "fallspecial"). In Super Smash Bros. Melee, air dodging caused a character to become helpless. Most characters also become helpless after using an up-special attack. While helpless, characters cannot perform any action except fast-falling, and characters are vulnerable to attack. Helpless mode is canceled by hitting the ground, grabbing a ledge, or being hit with an attack that causes the character to flinch. Additionally, several other special attacks enter characters into helpless mode after finishing the animations of the attacks while aerial. These moves include:
 * Dark Dive (Unsuccessful contact with enemy)
 * Dimensional Cape
 * Din's Fire
 * Drill Rush
 * Egg Roll
 * Falco Phantasm
 * Falcon Dive (Unsuccessful contact with enemy)
 * Fox Illusion
 * Gerudo Dragon/Flame Choke
 * Giant Punch**
 * Gliding after all midair jumps
 * Mach Tornado
 * PK Flash
 * PK Freeze
 * PK Thunder(if missed)
 * Quick Draw
 * Raptor Boost
 * Rocketbarrel Barrage
 * Rollout*
 * Squall Hammer
 * Super Jump Punch
 * Wolf Flash

* Only in Melee

** Only in Melee and Brawl

Land fall special and super dash technique
In debug mode, the state of the character when landing from this state is referred to as land fall special. Because airdodging enters this state, and wavedashing involves airdodging into the ground, when wavedashing was tried in debug mode, "land fall special" appeared for the character state. This led some players to believe that the "land fall special" designation was specifically designed for wavedashing and that developers put wavedashing in the game intentionally, further fueling the various debates over wavedashing's legitimacy. At one point, the myth morphed to where, instead of just land fall special, there was purportedly another debug mode designation, cited as "super dash technique", "superdashattack", or other variants, created solely for the wavedashing animation. All incarnations of this story have been proven false and should not be taken as evidence that wavedashing was intentionally put or left in SSBM.

In Brawl
Certain third jumps do not leave characters in a helpless state, and air dodges no longer cause helpless status. This completely changes the strategy of many characters.

Characters not put into a fully helpless state after using their Up Special:


 * Jigglypuff cannot enter helpless state in brawl. However, it's Up Special and Down Special last a long time and leave it unable to do anything during their duration. Once either of the attacks have ended, Jiggly can attack once more.
 * Mr. Game and Watch does not become helpless after using Fire, his up special, he just can't use the move again if the player manages to stop gliding with the parachute until he lands on a platform, grabs onto the ledge, or if he is attacked.
 * Meta Knight glides after he uses his Shuttle Loop, his up special. If not attacked out of it, the glide can eventually make him helpless. His other three specials, (Mach Tornado, Drill Rush, and Dimensional Cape), can also make him helpless.
 * Peach can enter helpless state by pressing down during her third jump but can cancel it by pressing up again.
 * Pit's Up Special only leaves him helpless if he is not attacked out of it.
 * When Kirby has the ability of any Standard Special Move that makes the player helpless in midair, (Giant Punch, Mach Tornado, PK Flash, PK Freeze, and Rollout in Melee) the same effect will happen to him. In Brawl, he can glitch to put in helpless state with his up special when landing on a moving platform that makes him get out of it before the animation of the landing special has finished.
 * R.O.B. cannot enter helpless state at all. But after using Robo Burner, his up special, he cannot air dodge.
 * Snake still can use all attacks besides Cypher after his third jump.
 * Sonic does not enter helpless after Spring Jump, his up special, although he can't use special moves after using it until he lands.
 * Yoshi reaches helpless state by canceling his Egg Roll in midair.
 * Zero Suit Samus's up special is a tether recovery that shoots straight upwards.

With the exception of Pit, Kirby, Yoshi, Peach, and Meta Knight, all the characters above cannot enter helpless state in normal play. With the exception of R.O.B, they can enter helpless by hacking the game; they have a helpless state, but no action can cause them to enter it. R.O.B. has no helpless state, and hacking the game to force him to enter helpless will cause the game to crash.

Trivia

 * Hitting a character with a thrown screw attack in Melee will cause that character to fall helplessly. This is useful if you can hit with the screw attack while an opponent is away from the edge, since it denies them all their remaining jumps and recovery moves.
 * In Brawl, nearly every playable character has a unique helpless animation, such as Luigi falling headfirst or Diddy Kong clutching his chest.
 * Characters can still Space Jump while helpless.
 * Peach is the only character in Brawl that can cancel helplessness. Fast falling after using her Up special will cause the player to be helpless, but pressing up will make her open her umbrella and allow her to float down again.