Drop canceling, also known as platform canceling is a technique introduced in Super Smash Bros.. It allows one to land back onto a platform immediately after platform dropping and hitting something with an aerial attack, cutting aerial time to minimum.
In 64 and Melee, while characters are in the air, their floor collision points move according to their animation, and are usually a short distance above the character's position. Since the floor collision point is level with the characters position while a character is standing on a floor, and usually above the characters position while in the air, characters would simply land back onto a platform immediately after trying to drop down if there wasn't a mechanism to prevent that. For that reason, the floor collision point is locked to same relative height as before the drop for a brief period when dropping from a platform, instead of letting it shift above the platform according to the animation. However, the lock period also wears down during hitlag while a character is frozen still. That can make the character maintain enough height such that its floor collision point still rises above the platform after the lock period ends, and result in the character landing onto the platform.
Drop canceling is usually done by following a platform drop as soon as possible with a quick aerial that hits something. Alternatively, getting hit by a cape or even a phantom hit immediately after a platform drop can result in a drop cancel. There are many deciding factors to whether an attack can be drop canceled on hit. Characters with low gravity are more likely to have aerials that can be drop cancelled, and can have larger windows for performing the aerial. Attacks have to hit quite quickly for drop cancel to be possible. Aerial attacks that shift the character's body upwards (like Falco's back aerial or Captain Falcon's up aerial) are more likely able to be drop cancelled than aerials with unsuitable low reaching animations.
After Melee, Drop Cancelling changed slightly. Although traditional drop canceling does not return in later games, certain stall-then-fall aerials and even special moves can emulate the effect, albeit with varying utility and effects. For starters, the startup lag isn't always shifted to one frame before. Overall, while it becomes slightly easier, the payoff is nerfed a smidgen. However, characters like PAC-MAN profit heavily off of this due to the combos it can enable. Characters such as Ryu and Terry can also drop cancel their command specials, which helps avoid accidentally dropping through platforms while using them.
How to perform
When used with aerial attacks that have little lag, a drop cancelled aerial attack can lead to lethal combos due to the incredibly small amount of lag. Normally quickly performed aerials have long airtime, since they're done when the character is rising up. Drop cancel completely cuts that lag. In Melee, regular platform drop includes 4 starting frames of crouching before the character becomes aerial and aerial attack can be done. Thus the startup of a drop cancel aerial via regular drop is similar to jump aerial, or even longer with characters that have shortest jump squat, such as Fox. With shield drop, s character becomes aerial immediately and can therefore attack on 2nd aerial frame. Thus drop cancels out of shield drop can be done even faster than jump aerials. However point blank shield drops usually require a setup that loses that speed advantage.
It is also possible to do this in Smash 64, as demonstrated through TAS style combos by Jpheal, and it is similarly incredibly difficult. However, it is only possible on rising platforms/diagonal platforms.
Applicable attacks in Melee
Unless noted, attacks have a one frame window. These apply to stationary platforms; for downward moving platforms, the window sizes may vary, and more attacks may be possible.
Pseudo Platform Cancel
When sliding off a platform you start falling with lower velocity than when dropping through a platform. This allows you to cancel many more aerials than a regular platform cancel because you effectively have more airtime. Here are 2 examples of this phenomenon.
In these examples, Marth and Falcon use aerials which cannot normally be platform canceled. They are hit in shield and shield DI towards the edge, which pushes them off the platform, then the knockback pushes them back on the platform.
These still require hitlag though, as hitlag allows the ECB to update (and thus become above the platform). Samus, however, has such low fall speed, that she can throw out a nair, have her ECB update, and be above the platform, without any use of hitlag.
Similar to drop canceling is the aerial interrupt: a technique in Melee that causes a character to land on a platform earlier by doing an aerial attack at a certain frame. The reason it works is that the character's environment collision box (ECB) is shifted downwards due to the attack's animation, making it connect with a platform and triggering the landing animation. It can be used to preserve enough ledge intangibility so that a grounded attack can be carried out whilst being still intangible. Its use can replace the need to air-dodging onto a platform since the aerial interrupt is the fastest possible way to get onto a platform from under it.
Applicable attacks in Brawl
Applicable attacks in Smash 4
Applicable attacks in Ultimate
Largely the same as in Brawl and Smash 4 in execution.