When used, Lucario stops for a brief moment, and then it rushes in the direction chosen. It is possible to change directions during the dash (where Lucario will appear to "bend" through the air), as well as being able to wall cling if it comes in contact with a wall, making it a very useful recovery move. Lucario has high air speed while using this move, and it has a large sweet spot, making ledge-grabbing easier.
Unlike in Super Smash Bros. Brawl, in Super Smash Bros. 4 the distance traveled by Extreme Speed increases as Lucario's damage rises, which makes it a stronger recovery at damages where it's needed. At 0%, the distance gained is comparable to Brawl's, but at 190% the distance gained becomes incredible, to the point where Lucario can easily overshoot the stage if it isn't careful.
The speed Lucario gains doesn't end when the move ends, as it keeps Extreme Speed's velocity a second after the move ends, making Lucario move even further if the move ends in the air - a ground-hugging full aura Extreme Speed travels 3/4 of Final Destination, while an aerial Extreme Speed can cover even more than Final Destination's entire length if it ends in the air. This, along with Extreme Speed's ability to change direction in mid-flight and inability to land before the move completes, can make the move especially difficult to aim at high percentages as the sheer speed at high aura is difficult to control. In essence, the move becomes a double-edged sword at max aura: Lucario can easily recover from anywhere offstage, but can as easily underestimate the distance it travels and shoot off the other side of the stage.
As of Smash 4, Extreme Speed deals damage to opponents only when the move ends, unlike in Brawl, where it dealt no damage. This gives the move some offensive capabilities, as it can actually KO if Lucario and its opponent are at 120% or more. However, the move now has two seconds of landing lag if Lucario ends the move in the air, making it incredibly unsafe if the opponent is nearby; this can be remedied by ending the move parallel to the ground or making Lucario hit the stage face-first, which cuts ending lag to half a second.
ExtremeHogging is the use of Extreme Speed to quickly grab the edge to edge-guard a player attempting to grab it. If the player uses the move but holds down as the direction, Lucario zooms across the floor to the left. By going over the lip of the ledge, still holding down, Lucario will almost instantly grab the ledge. If the player wants to go right, it's a little harder, since right-and-down must pressed diagonally.
Special Move customization was added in Super Smash Bros. 4. These are the variations:
Use by other Pokémon
In the Pokémon games, Extreme Speed was introduced in Generation II as a more powerful version of Quick Attack; in that generation, it was the signature move of Arcanine. It is a physical Normal-type attack with 80 base power, 100% accuracy, and a +1 priority in Generation II-IV and a +2 priority in Generation V and VI, meaning it will usually go first if there is no other higher priority attack being used as well, regardless of the user's speed. In return for being exceptionally fast, this attack only has 5 PP (can be upgraded to 8 PP maximum), so Extreme Speed can only be used 5 times before running out of power.
Lucario can learn Extreme Speed by leveling up, and is one of the very few non-legendary Pokémon able to learn the move by any means.
Rayquaza can also learn the attack naturally by leveling up, and is instead one of the Dragon-type Legendary Pokémon along with Zygarde as of Generation VI to learn it like so.
In Generations II-V, the move's name was formatted "ExtremeSpeed", and this spelling is also used for Brawl. Since the Generation VI Pokémon games reformatted the move's English name as "Extreme Speed", the move's name was similarly changed for SSB4. Despite this, the official Miiverse posts pre-release continued to refer to "ExtremeSpeed" without a space.
The Japanese name of the move is derived by the term "Shinsoku" (神速), a Japanese term for swiftness, but literally can also mean "godspeed".