Crown landing is a technique discovered by Plague von Karma, Crown Landing enables King K. Rool to significantly reduce - or if frame perfectly, completely erase - his landing lag. This is executed in two ways, referred to as the "No Crown" and "Crown Pickup" variants by the playerbase.
To execute the No Crown Variant, the player must input Crownerang when the Crown isn't on K. Rool's head 45-35 frames before landing. This will have K. Rool land a few frames before the "No Crown" animation ends (which lasts 36 frames), converting into his landing lag in an unnatural way. If done perfectly, this will leave K. Rool with either 1 frame of landing lag (rather than 6 from the hard landing), or snap him into his idle animation. Thus, it is possible to land and then immediately perform another action.
To execute the Crown Pickup Variant, the player must collect the Crown 35 frames before landing. This will almost always leave the player with 1 or 0 frames of landing lag, being much more generous - albeit situational - than the No Crown Variant. The biggest benefit of this is being able to use Crownerang immediately after landing, enabling a lot of horizontal pressure reminiscent of Crown Squatting. This enables a lot of pressure around Battlefield's platforms, as they provide a very safe way of executing this tech.