Tumbling (or DamageFall internally in Melee and Brawl files) is an airborne state that a character may enter after being hit or pushed in certain ways; for example, edge slipping can cause a character to tumble. A tumbling character can easily be identified by their defensive, rotating animation. Characters may tumble after being hit through the air by an attack with strong enough knockback, footstooled in midair, pushed off a ledge, after walking off an edge while carrying a crate or other heavy item, or by sliding off of an edge while shielding.
In the original Super Smash Bros., the minimum knockback that must be inflicted to cause tumbling is roughly 60 units and in later games, this would be increased to around 80 units.
The benefit from tumble compared to non tumble hitstun varies from game to game. In Smash 64 and Melee, tumble is not beneficial since it leaves the opponent in more hitstun than a non tumble state. In Brawl however, tumble leaves the opponent at a bigger advantage than a non tumble state. Tumble enables the opponent to perform hitstun cancelling (and subsequently momentum cancelling) which is not possible in a non tumble state. It also enables the opponent to DI which they cannot do from non tumble hitstun starting from Brawl and the gravity penalty also now takes effect once the opponent enters tumble. This enables characters with high gravity (such as Fox) to fly much higher once they enter tumble preventing chain grabs and strings to connect against them. In Smash 4, hitstun cancelling's effect was greatly reduced making tumble less beneficial than in Brawl although it still has the same advantages besides hitstun cancelling. With Ultimate homogenising the effect of falling speed and gravity against moves with an angle between 70°-110°, tumble has become less beneficial again although it still enables the opponent to DI.
Actions possible while tumbling
If tumbling characters hit the ground without teching, they will land into a lying position and must then use a floor recovery. Characters undergo a flopping animation upon hitting the ground before they can use their floor recovery, leaving them vulnerable for a short while.
The tumbling animation is used after a shield jump, though no action can be performed during this time. It is also used at the end of Olimar's Final Smash (after emerging from the Hocotate Ship), but Olimar will be unable to do anything other than move horizontally.
Reeling (known as DamageFlyRoll internally) is an alternate hitstun state characters can experience if hit by a move with enough knockback to cause tumbling, denoted by their helix motion while flying. In all games, reeling has a 30% chance of occuring, and only if the target has at least 100% damage; this is checked after they get hit, so a tumble-inducing attack that brings them from below 100% damage to that amount or higher can cause reeling as well.
Reeling's differences from the usual knockback animation are only aesthetic, though due to the change in animation shifting the character's hurtboxes, it can rarely cause them to get hit by attacks that would have otherwise missed, or vice versa. The exception to this is in Smash 4, where reeling reduces hitstun inflicted on the target by one frame, and prevents them from teching on the ground until their hitstun cancel window starts. While the former difference is negligible, the latter effectively gives characters a random chance to be unable to avoid a knockdown, allowing for certain KO setups, such as Fox's forward tilt or neutral aerial into an up smash. However, and only in Smash 4 as well, reeling allows Cloud to tech walls and ceilings if he is hit near the apex of Climhazzard, where teching is otherwise impossible. In Ultimate, these discrepancies are removed, causing reeling's differences from the standard pre-tumble animation to be purely aesthetic again (aside from hurtbox placement), and it additionally cannot happen if a character is launched from behind.
Due to his two-dimensional nature, Mr. Game & Watch has a unique reeling animation, spinning in a cartwheeling motion instead of a spiraling motion. Steve also has a unique reeling animation, which is just his tumbling animation with his body oriented in the direction of his knockback.
Some attacks in later games are capable of forcing reeling regardless of the target's damage percentage, namely the tornadoes in Hyrule Castle (from Smash 4 onward) and PictoChat 2, as well as the Mii Swordfighter's Gale Strike in Ultimate. The Bullet Bill item also puts characters in state similar to reeling after its use; however, it does not end naturally, and can be canceled with an aerial attack, an air dodge, or by landing.