Wavedashes
A wavedash is a commonly used technique in Celeste that allows the player to perform a small but long jump while also regaining a dash. It's introduced in Farewell, right after passing the heart gate, and is frequently required in order to pass a lot of rooms later in the chapter.
Functionality
Wave dashes are used for a quick boost of high velocity which throws the player forward. Wavedashes are mainly used in more difficult maps (such as Farewell) or for speedrunning purposes (because of the speed they give). Wavedashes give Madeline less height than a normal jump (about 3/5 of a normal jump), meaning it can still be used even if there are spikes close to Madeline's head. Stringing wavedashes (doing one after the other in quick succession) makes for different types of ultras.
Other variants
Bubble Wavedashes
Bubbles allow players to stall in mid-air for a short time, and if they're at a specific height, Madeline will be able to perform a wavedash if the player aims in a down-diagonal position and jumps off of the ground before the dash momentum wears off. Although the vanilla game never requires you to do this trick, it's often used by speedrunners or in custom maps, where they're often used as setups for consistent wavedashes.
Extended hyper
For short, extended hypers are a grounded variant of a wavedash. While the game teaches you to do wavedashes from a specific height, it's not necessarily required, as long as you jump when Madeline's hair flashes white. The effect is the same as with a regular wavedash, but it's an alternate way to perform it for players who don't feel comfortable doing it from air. Its disadvantages is that it's much more difficult to perform and to get consistent with, since it relies more on muscle memory than visuals. It can be done on any platform which is 2 tiles or larger, although doing it on 2 tiles requires even more precision.
Generally, wavedashes should be used instead of extended hypers, if possible.
Reverse wavedash/extended hyper
While performing a wavedash or extended hyper, a player can quickly switch directions while dashing (dash in one direction and, while moving, hold the opposite way) to do a backwards jump. It gives the same speed and height as a normal wavedash. This move is useful for places where there is not enough room to do a normal wavedash.
Extended demohyper
An extended demohyper is a type of extended hyper that's performed by jumping after doing a demodash from ground, usually used with a demo bind. A demohyper behaves nearly identically to its normal variant, except for it giving Madeline slightly more distance due to the player doing a straight crouched dash instead of a diagonal one, as well as it allowing players to do a demohyper from mid-air. Due to the technical difference, it's usually not recommended to use demohypers from ground, but they're often used by speedrunners to perform the move from mid-air. If you intend to do a demo hyper mid-air, begin your demo hyper from further back. This will refill your dash.
Trivia
- Even though Farewell teaches the player how to do wavedashes, the chapter can be completed without doing a single one, as well as without any extended hypers, but a lot of the skips require other, often more difficult solutions such as tight Superdashes or Ultradashes.