The Knee Smash, also well known as The Knee or the Knee of Justice, (and a variety of other nicknames involving the term "knee"), is Captain Falcon's forward aerial in the Super Smash Bros. series and in Super Smash Flash 2. It is an extremely powerful, quick, low-trajectory KO move often used at the end of Falcon's combos and for edge-guarding. It is not present in Super Smash Flash due to the limited number of attacks that characters were given.
The move has properties similar to a sex kick due to the sweet spot being in the initial frames of the attack. If sweet spotted, the opponent will be electrocuted and hit with great knockback. If sour spotted, then the move will be a weak semi-spike, but it can be followed up with other attacks including a sweet spotted Knee or help in gimping opponents recoveries in certain situations. Captain Falcon can SHFFL this attack so he can follow up with different aerials to help in his combos. It is considered one of the best aerial attacks and is one of the strongest forward aerials in the game.
It can be utilized in many of Captain Falcon's aerial combos, being an excellent combo finisher and versatile part of his combos alike, as well as a generally great KO move and edgeguarder. At low percentages, the move can chain into self or when sweet spotted can be followed up with a Falcon Punch to perform the Sacred combo.