Buried is a status condition that can be inflicted by attacks with a bury or plunge effect. It debuted in Super Smash Bros. Melee and has appeared in every subsequent game. A buried character is embedded in the ground, with the visible part of their body surrounded by churned dirt.
In Super Smash Bros. Ultimate, characters now have two buried poses, upright and upside-down. Fighters are normally buried upright, but King K. Rool and R.O.B.'s down throws will bury the thrown fighter upside-down. The upside-down buried pose is also used during the animation of Lucas's down throw, although it does not cause the buried condition. (While Lucas's down throw does show a character buried upside-down in SSB4, in that game it uses a character's grabbed animation rather than a specific buried pose.) The difference between being buried upright and upside-down is purely aesthetic.
Any fighter on the ground hit by an attack with a bury effect will be buried. In SSB4 and Ultimate, a character that is lying down cannot be buried, unless they are lying down due to Snake's down throw; however, a character who has tripped can be buried. In Melee, a character lying prone cannot be buried, but they can in Brawl. If a fighter cannot be buried, they will simply take knockback as usual from the bury attack.
Examples of attacks with the bury effect are Donkey Kong's Headbutt, Villager's down smash, and the Poké Ball Pokémon Togepi's Magnitude. Additionally, the Pitfall item will bury a fighter, but the Pitfall item uses the plunge effect rather than the bury effect.
A buried fighter is immobilized until the status wears off. While buried, they cannot be grabbed or be re-buried.
The amount of time a character remains buried is dependent on that character's damage percentage; the higher the number, the longer they will be stuck to the ground. This duration can be decreased by button mashing. If the ground below the character disappears, they are automatically unburied. When the buried condition fades, the released fighter gets some invincibility frames.
In Melee, buried characters remain stuck in the ground until the effect wears off or the ground disappears. From Brawl onward, a character hit by a move that deals more than 100 units of knockback will freed from being buried and launched as usual. In Brawl and Ultimate, the amount of knockback taken does not get reduced, allowing for reliable, early KO setups on buried characters; however, in Smash 4, it is equal to 0.7x of the knockback that would have been inflicted otherwise, drastically weakening the effectiveness of such setups. In Ultimate, attacks performed without unburying the opponent retain their properties when the effect wears off, including neutral attacks and meteor smashes.
The boss Rathalos (but not as an Assist Trophy) is affected by Pitfalls, having its own unique buried appearance with a very large amount of churned dirt surrounding it. It cannot be buried by attacks with the bury effect, however.
Super Smash Bros. Ultimate
In Ultimate, the Bury formula is 75 + 1.5 * KB + 0.5 * Opponent's %. This will calculate the mash frames, which are deducted based on how fast the victim can mash.
Donkey Kong's Headbutt is slightly different, with two variants based on an aerial or grounded hit.
There are two types of mashing: Directional, and Button Mashing. These mash values are specific to Bury itself, but can also be applied to grabs, command grabs, Sleeping, and Wrecking Crew's barrels. Otherwise, they are different.