Down Air Attack

Lucario's down aerial, which negates momentum.

Marth's down aerial.

The down aerial (abbreviated as "dair", "DAir", "d-air" or "ADA") is an aerial attack that is performed in midair by pressing the A Button, and tilting the control stick downwards. Its official term varies between titles, where it is known as a "Down Midair Attack" in Super Smash Bros. Melee, and a "Down Air Attack" in Brawl. Sometimes used as spikes.

Characters' Dairs

• Mario: The famous Mario Tornado, replaced by the F.L.U.D.D. as a down special, is now his dair.
• Luigi: Spins rapidly in place. Multiple, effect-varying hitboxes surrounding, butt, feet, arms, and torso. If butt connects and sweetspots, it becomes a strong spike.
• Peach: Thrusts legs rapidly below herself at a slight angle.
• Bowser: Flips upside-down and rotates around inside his shell. Racks a lot of damage, and has an additional hit upon landing, which helps to keep opponents from taking advantage of the large landing lag.
• Donkey Kong: Thrusts leg below him to always meteor smash while performing a strong-man pose in midair.
• Diddy Kong: Clasps one hand over the other and spikes always.
• Yoshi: The greatest damage racking aerial in the game. Flutter kicks super fast below him. Deals 33% and spikes after last hit.
• Wario: Flips upside down and rotates once or twice. Interestingly enough, when the move connects, he makes contact 7 times.
• Link: Kneels above his sword with it upside down. Extremely powerful, incredibly long duration, and no startup lag. There is noticeable ending lag though, when he lands on the ground and has to yank it out. Also, if he hits an opponent, Link will hop up in the air (unless Link is fastfalling).
• Zelda: Thrusts leg once below her vertically. Spikes if sweetspotted. If sweetspotted, electric sound, pause, then foe down-rockets.
• Sheik: A Stall-Then-Fall. Sheik bends her body behind her center of gravity and leans leg out below her. Minimal knockback, and is dangerous, but it is very slow.
• Ganondorf: Jams legs underneath him. Multiple hitboxes, but the meteor smash will always remain the same. Called "The Stomp" for being one of the most powerful Meteor Smashes in the game - in fact, if it hits a grounded opponent, they can bounce off the ground and be Star KO'd. Has an electric effect.
• Toon Link: An incredible priority Stall-Then-Fall. Similar to Link's, although rockets downwards without stopping and can spike near beginning few frames. Dangerous to use when not above ground, but if you have more lives than foe, risk one to spike them as they recover. Like Link's, it bounces off the opponent; after the bounce, it works like a normal aerial attack.
• Samus: Flips 90 degrees forward and faces the screen while swinging arm cannon in a 180 degree arc below her. Sometimes a meteor smash, but quite slow.
• Zero Suit Samus: A Stall-Then-Fall. Turns body in a linear form, then propels downward. If foe is hit in the air, they are carried down until they are knocked away once in contact with ground. Might make food for thought about "Zerocide" if it is used on a foe in the air and is carried downwards until both ZSS and foe KO.
• Pit: Swings both halves of bow downwards. Strangely, this move incurs upwards knockback most of the time.
• Ice Climbers: A half Stall-Then-Fall. Both position hammers below themselves and fall downwards a very slight distance. Knockback is upwards and a bit diagonal.
• R.O.B.: Pauses momentarily, then blasts boosters powerfully downwards. Will spike if hits. Can be used to stop vertical momentum, but is hard to use correctly, and will propel a bit upwards if incorrectly used.

Some down aerial attacks spike the opponent.

• Kirby: Spins around in multiple circles. Legs produce most damage and knockback. Can meteor smash.
• Meta Knight: Swings sword below him. Looks like Marth's dair, but will never spike. It can semi-spike though. Can be used on the ground (short-hopped) to set up a kill by edgeguarding.
• King Dedede: Spins hammer around under him for multiple hits. Works well in the ascent of a ground jump.
• Olimar: Arcs a Pikmin below his knees. Similar to bair and fair. If the enemy is directly below Olimar, it becomes a meteor smash, with power varying by Pikmin - purple, yellow, and red are very strong, blue is of mediocre strength, and white is weak.
• Fox: Spins legs around, a bit diagonally, hitting multiple times. Weakest Spike in the game after last hit. Similar to Falco, Kirby, or Jigglypuff's dairs. Useful when shorthopped for combos.
• Falco: Same as Fox's, except only one hit, not several. No lag, and very strong meteor smash when hit near first to near-last frames. Easy to spike with.
• Wolf: Similar to Diddy Kong's. Laggier, though.
• Captain Falcon: Same as Ganondorf's, except quicker, and doesn't spike as powerfully near nipples. If hit near chest, slanged as nipple spike.
• Pikachu: Like his fair, but downwards with only one hit. High lag when landing.
• Squirtle: Same as Mario Tornado, but is better vertically ranged because of Squirtle's long tail.
• Ivysaur: Blasts his bulb below himself. Surprisingly, does not launch Ivysaur upwards, but stalls him in the air, like Lucario's dair. Can be a powerful spike if the foe is right beneath Ivysaur.
• Charizard: Flicks tail out of hitboxes and stomps his feet down. Deceptively strong, and meteors.
• Lucario: Blows up two bursts of aura beneath its foot. Stalls all frames of vertical momentum and can be used to delay it. Very powerful move in general and can be used in multiple ways because of immobility.
• Jigglypuff: Spins around. Identical to Kirby's. Absolutely no knockback unless at %s above 200.
• Marth: Swings sword beneath his legs. Can spike if sweetspotted, but has some poor landing lag in Brawl.
• Ike: Faces screen while swinging sword down. If hits blade, spikes. One of Ike's four spikes.
• Ness: Jams foot down. Very laggy, but is an extremely powerful meteor smash.
• Lucas: Four quick downward kicks. Can rack up to 20% damage, each kick doing exactly 5%. A medium power spike served with last kick. Easy strategy by using on vincible edgeholding foe. Simple spike use out of immediate initial jump ascent.
• Mr. Game & Watch: A Stall-Then-Fall (Donkey Kong Jr.) Grabs a key and plunges downwards. Upwards knockback; similar in most ways to Ice Climbers' stall then fall. Can be aimed slightly to the side and can be canceled in the middle with Fire. Can also perform the Stall-Then-Fall Glitch along with Toon Link. Is a spike if the enemy is directly under him, and if you tap down on the d-pad after executed, the move will slow.
• Snake: Launches four subsequent kicks below himself. Similar to Lucas', but more damage, knockback, and doesn't spike. Can be used very well in a short hop for a medium-high percent kill on a grounded opponent.
• Sonic: A Stall-Then-Fall. Lasts a long duration, but has high landing lag.

Notable characters' down aerials

• Captain Falcon's down aerial, a spike in 64 and Melee.
• Falco's down aerial, a fast spike in Melee and Brawl with high range vital to Falco's pillar.
• Fox's down aerial, notorious for its use in his infinite combo.
• Wolf's down aerial, a spike similar in strength and effect to Falco's "Dair" spike, although it takes a split second longer to complete.
• Lucario, Ivysaur, R.O.B.'s down aerials all stop vertical momentum, making those moves good for recovery.
• Mario's down aerial, officially named the Mario Tornado in Super Smash Bros. Brawl.
• Yoshi's down aerial, a very damaging move which can take up to 40% with its multiple kicks.
• The Ice Climbers, Mr. Game and Watch, Shiek, Sonic, Toon Link and Zero Suit Samus' down aerials, all of which are Stall-Then-Fall aerials in Brawl. Also, if Toon Link's down aerial hits a foe, he will "pogo-hop" and allow him to hit another enemy again.
• Ness's down aerial, which is a meteor smash.
• Ganondorf's down aerial, a powerful meteor smash.
• Marth's down aerial, possibly the most feared with its speed and range in melee and brawl.
• Diddy Kong's down aerial, once connects, is hard to recover from.

Notes

• According to the SSBB Prima Official Game Guide, Wolf's Down Aerial Attack is a "Dair" spike, and is indeed similar to Falco's "Dair" spike.