Marth Tech: Wavedash
Description / How To Perform
Second only to 
Dash Dancing, Wavedashing is an essential method for positioning yourself on the ground. Performed by air-dodging diagonally into the ground, a Wavedash causes your character to slide along the ground without changing the direction they are facing.
Wavedashing towards an opponent allows you to quickly attack them with grounded moves that cannot be used while dashing. Wavedashing back can be used to retreat from your opponent while still facing them, leaving more counter attacking options available to you. Wavedashing can be performed while dash dancing to create tricky and difficult-to-predict movement. It's also useful for grabbing the ledge of the stage to edgeguard opponents.
Difficulty: 
(Intermediate)
Usefulness: (Essential Skill)
Extra Info
Although it's ok to learn Wavedashing by airdodging at a 45 degree angle downward, there are many other wavedash angles/distances that you shouldn't ignore. Most importantly, a perfect wavedash that achieves the maximum sliding distance is done by tilting the analog stick very close to horizontal rather than diagonally down/right. This can be difficult to learn, but it's better to start early.
If you Wavedash into the edge/ledge without releasing the analog stick angle while facing away from it, you will slide off while retaining your momentum. If you Wavedash while facing the edge/ledge and release the angle, you will stop in place and start a "teetering" animation. To Wavedash towards an ledge/edge and slide off you must hold towards the ledge/edge after inputting the Wavedash.
Marth has the fourth longest Wavedash and
Waveland in the game. His Wavedash length is only exceeded by Mewtwo, Ice Climbers, and Luigi.