A launch is an extremely fast movement technique that allows the player to trick the game into turning deceleration into acceleration with no cap. Due to this heavy acceleration, launches can also often prompt wall zips, allowing for calculated and precise movement throughout the entirety of the castle in a matter of minutes. Below are detailed different types of launches.
Empty Launch: Near a ledge, move away from the ledge, stop moving away, then as you are slowing down (7 frames for Juste) dash toward the ledge. This will propel Juste off the ledge for a short time, giving him the furthest distance he can achieve for a coyote jump, allowing for tricks such as platinum tip early or skull skip.
Whiplaunch: Begin with an empty launch, but within 6 frames of dashing, use the whip or a subweapon. This lets you accelerate for every frame that the launch continues. To continue the acceleration after the whip or subweapon, you have 6 frames to whip or use a subweapon again. The acceleration continues to be applied until you either miss those 6 frames, or land on the ground, or jump. After the acceleration stops, you start to decelerate and you can't start accelerating again. Whiplaunches are the basis of almost every zip and OoB clip that Harmony of Dissonance has to offer, and is quite possibly the most importand trick in the game along with its twin, the candle whiplaunch.
Candle Whiplaunch: Use your double jump near a candle, then move toward it. Release forward, and while Juste is slowing down (8 frames) input a divekick with down+A. If done correctly, the divekick should move diagonally despite only being done with a down input. Aim the divekick to hit the candle, and one frame after the divekick breaks the candle, use the whip. This will provide the same acceleration as a ledge whiplaunch, but with much more accessibility due to the abundance of candles as well as the fact that a candle whiplaunch can be performed on enemies as well. The tradeoff for this accessibility is the much more strict frame window of the whip timing, but that's not to say it can't be consistent.
Different Accelerations: Launching works by carrying over deceleration to the other direction making it acceleration. This means that the acceleration of the launch will be different depending on the deceleration that's carried over. Those decelerations are:
Juste on ground: 1/4 pixels per frame per frame.
Juste in air: 1/8 pixels per frame per frame.
Juste in air with floating boots: 1/32 pixels per frame per frame.
More Launch Details: You can extend the time before you start decelerating a little by throwing a subweapon right before you land on the ground. That way, the deceleration starts only after the throwing animation ends. During the throwing animation on the ground, you don't accelerate or decelerate, so the speed stays the same. However, deceleration on the ground is twice as fast as deceleration in the air. So the best strategy to keep the highest speed possible in a launch is typically to throw a subweapon right before landing and then jumping as soon as possible afterwards. It doesn't make a difference on which of the frames that you dash or whip as long as you get the launch out of it, unless it changes when the launch ends. The only things that decide whether or not you get into a wall is are the position you launched from, when the accelerating period ends, what kind of deceleration is applied after it ends, and the subpixels you had when you started.