Crown canceling is a technique in Super Smash Bros Ultimate. If an uninterruptible animation such as an attack or knockback is in effect while the crown is coming back, K. Rool's head will flash green as the crown appears on his head. This completely skips the 17 frame crown pickup animation, leaving K. Rool less open for punishment. This is referred to as Crown Cancelling by the K. Rool playerbase, and there are many ways to exploit this.
For example, by using Crownerang to force shield on the opponent, K. Rool can run in with a dash grab to not only Crown Cancel, but also get a grab off of it. This is extremely potent for making the opponent not shield, and force approaches later in the game. A successful grab can potentially close out a stock if the opponent is at a high percentage thanks to down throw's kill confirms, so this is useful to keep in mind when trying to break the opponent down.
Using up tilt or forward tilt with the tech is also very useful for punishing a reckless approach, as a lot of opponents tend to try and jump in when Crownerang is being used. Both of these also have a chance of sending an opponent into a returning Crown while also initiating a Crown Cancel, which can lead to a very long combo. Forward aerial is also considered to be one of the safest offensive Crown Cancels, as it is often enough to gain advantage and stage control just by landing it.
Shielding is often considered to be one of the better options if Crownerang is misused, as it usually makes an opponent such as Lucina attempt to engage with a forward aerial and press advantage. This can allow for a very heavy punish from K. Rool. Staying in shield while waiting for it to come back is not recommended, however. The fact spotdodging can Crown Cancel makes this a great defensive measure against tomahawking opponents as well, especially considering how King K. Rool's spot dodge is the same as the likes of Bowser and Ridley's. As a result a potential punish can turn into a Down Tilt hard punish on characters with worse grabs (most notably Palutena), and likely a KO. Even if this doesn't work, King K. Rool's dash attack works on almost every character in the game if he spot dodges correctly.
There is a sub-category of this tech known as Crown Squatting, discovered by Plague von Karma, which involves the crown landing on K. Rool during his jumpsquat. If done on the first frame, there will be no green flash to indicate a successful Crown Cancel. This aids in confirming back aerial kill confirms from a returning crown, or generally increases momentum in the match by saving 17 frames. The most notable application for this is to immediately use Crownerang again, allowing King K. Rool to control the stage in a surprisingly efficient way.
List of moves that can initiate Crown Cancel;
Hard and soft landing lag does not initiate a Crown Cancel, although a move's landing lag will.