Landing lag glitch
The landing lag glitch, also referred to as recovery carryover lag or RCO lag, is a glitch in Brawl and Smash 4 that causes certain special moves that place the user into a helpless state to have their landing lag carried over. If the user grabs an edge or gets hit after using a given move, once they land on the ground, they suffer the landing lag that would have been applied in their helpless state. The only way to avoid the lag is to drop from the edge and use a mid-air jump without grabbing the edge again.
The glitch cannot be avoided with specials that do not cause the character to become helpless and never disappear until landing on the ground; however it can be "overruled" by using an aerial that has landing lag, though with 35-40% more landing lag than would usually get for landing with that aerial. Preferably, one would use an aerial with lag to partially override the glitch, but still suffer more lag than the aerial would provide.
Characters affected by the glitch
Except for Donkey Kong and Bowser, who both get a relatively small extra two frames of lag, all characters listed have 15 frames for soft landing. Hard landing values are listed below.
In Smash 4
While the glitch no longer occurs after grabbing a ledge, most characters suffer a varying amount of landing lag if they are hit after the execution of their up special moves, but before they land. Additionally the amount of lag suffered is now equal to the animation length of the landing animation for the character, be it from hard/soft landing or an aerial. Captain Falcon, Ganondorf, and Zero Suit Samus also remain affected by RCO lag after they connect with Falcon Dive, Dark Dive, or Flip Jump respectively and land on a platform. Any aerial used in an attempt to override the RCO lag will also experience increased landing lag, like in Brawl, while if the aerial autocancels the RCO lag is experienced. However in some rare cases, such as Captain Falcon's up aerial, the landing lag received can actually be slightly less than the RCO lag they would have received otherwise. Some moves, particularly multi-hitting electric moves like Mewtwo's neutral aerial or Pikachu's forward aerial, induce extra landing lag on the character they hit if they end prematurely.