L-canceling, or Z-canceling in Super Smash Bros. (officially called a smooth landing), is a technique in Super Smash Bros; Super Smash Bros. Melee, and Crusade for reducing the length of recovery animations after landing on the ground while performing an aerial attack. By pressing Z, L, or R (hence the names "Z" and "L") slightly before landing on the ground, players can reduce their recovery time, a significant decrease that greatly increases a character's maximum rate of attack. L-canceling was no longer available in Super Smash Bros. Brawl though auto-cancel was in.
In Crusade, L-Cancelling returned, making Combos much more varied.
Note: This applies to Crusade in version 0.9-Test and prior versions. In the 0.9 release, L-cancelling was removed in exchange for generally shorter landing lag on all aerial moves.
(Another note: In Super Smash Bros. Melee, Mr. Game & Watch's neutral air and back air attacks couldn't be l-cancelled for unknown reasons. In Crusade, Fox's down air and Meta Knight's neutral air cannot be l-cancelled either, although these are for competitive balance reasons.)
Short Hop Fast-Fall L-Cancel
Short hop fast fall lag-cancel, commonly abbreviated as "SHFFL" (pronounced like the word "shuffle"), is a combination of advanced techniques that, for most characters, results in the quickest and least laggy way to jump and perform an aerial from the ground in Super Smash Bros. Melee. A SHFFL, per its name, comprises a short hop, a fast-fall and an L-cancel, and an aerial attack that occurs while the user is in mid-air.
When teaching advanced techniques to new players, Smashers often emphasize the importance of SHFFLing because the technique reflects a mastery of several important advanced techniques. SHFFLing is highly useful in battle because its speed allows players to use aerial attacks in tandem with ground moves.
Chronological button input:
X/Y/up slightly A/A+direction/C Down L, R, or Z
The last one can be skipped for certain aerials if the aerial is performed very early. You can go to training mode with Marth and set the speed to 1/2 or 1/4. Do a short hop and, as fast as possible, a nair (or fair). Fast fall it and L-cancel it. Repeat it without the L-cancel. The player will notice that both variations will take the same time. This is because the attack animation ends when Marth is still in mid-air and will fall down just as the player hadn't performed an attack. Since jumps can't be L-canceled, it makes no speed-wise difference whether the player presses L/R/Z or not. However, pressing one of these button will probably result in a airdodge or a shield, depending on whether it is pressed before or after the landing. Thus it is possible to do fair-to-waveland and likely combos, although there are few situations where it can be used effectively. Performing the aerial early enough to skip step 4 is simply described as "Early SHFFL".
In Crusade, SHFFL makes a return, though it's difficult to perform due to use of keyboard controls, but it functions the same as in Melee. Snake makes good use for this due to his laggy aerials and short hop combined with fast-falling speed.