- Not to be confused with the first hit of Solid Snake's Forward Tilt.
The Knee Smash (also known as "Falcon Knee", "The Knee of Justice", etc.) is Captain Falcon's Forward Aerial in every installment since Super Smash Bros. Melee. It is an extremely powerful low-trajectory KOing move, often used at the end of Falcon's combos and for edgeguarding.
Super Smash Bros. Melee
In Melee, this move is considered among the best in the game, due to its short lag time and powerful knockback when sweetspotted. Many combos and strategies for Captain Falcon end with a Knee, which deals up to 18%, under circumstances not influenced by items, stale-move negation, or stage effects. In addition, if sweet-spotted at 60% or so, professional smashers can follow it up with an aerial Falcon Punch in the deadly Sacred Combo. The move is very useful for edgeguarding due to semi-spiking the opponent.
The Knee Smash has two main hitboxes. The initial hitbox is Captain Falcon's primary KO option and is accompanied by an electrical pulse, but only lasts a few frames. This hitbox is considered the attack's sweet spot, though the move functions more like a sex kick. The second hitbox lasts much longer and lacks the damage and knockback of the sweet spot. This is often called a soft knee, or weak knee. Due to the Knee Smash's low lag, professional smashers can use it as a launcher into another aerial attack, often a sweetspotted Knee Smash.
Super Smash Bros. Brawl
In Brawl, the knee has been nerfed as its sweetspot hitbox only lasts 1 frame and requires actually landing the knee hitbox, unlike in Melee. Its hitlag lasts about a second, much longer than in Melee. A sousrpotted Knee Smash can now trip grounded opponents and the move is still useful for edgeguarding poor recoveries like Link's, but the changes to Brawl's physics make the sourspot less effective for combos. He can set up a sweetspoted Knee if he uses it after grab releases on Wario and Ness. It also has a damage increase (it now deals 19%), making it ever so slightly stronger despite its reduced knockback. The sourspot deals less damage, however.
Super Smash Bros. for Nintendo 3DS and Wii U
In Super Smash Bros. for Nintendo 3DS and Wii U, the move is largely unchanged from Brawl, aside from the fact that it is easier to combo into and much more versatile overall due to the changes to hitstun and his up aerial. The move also receives an ending and landing lag nerf and can no longer autocancel in a short hop however.
Though Ganondorf is Captain Falcon's clone, his Forward Aerial is not a Knee, but instead an arcing downward punch resembling Mario's forward aerial in all of his appearances, nicknamed "Skull Crusher". In Melee, it has the same amount of start-up frames as Falcon's Knee, but has much higher base knockback at the cost of knockback scaling and damage, slightly lower ending lag, much more range, no semi-spike angle and a consistent hitbox instead of sweetspot and sourspot hitboxes. In Brawl, it is much slower, has reduced range, altered knockback, and has 2 hitboxes instead of one with less difference in damage and knockback compared to the 3 hitboxes of Captain Falcon's Knee (2 of them being much weaker than the sweetspot both in terms of damage and knockback). In Super Smash Bros. for Nintendo 3DS and Wii U, the move's sweetspot and sourspot are even closer in terms of power, but the move received no changes otherwise. To some players, the attack is also nicknamed "The Punch".
- The Knee Smash is one of only four knee-based attacks that are not pummels (the other three being the third hit of Falcon's Neutral Attack combo, Zero Suit Samus's dash attack, and the first hit of Snake's Forward Tilt).
- Captain Falcon's wireframe and alloy counterparts variation of the knee can also be sweetspotted in the same manner as the original, but for less knockback, damage, and the lack of an electrical effect.