Here are a handful of moves that will show up during KSS speedruns.

No Ability

Sliding

Sliding is mainly used for gaining extra speed before running off a ledge.

Sliding on its own is significantly slower than running, since the slide takes a while to complete and slows Kirby to a halt near the end of it. Sliding off ledges allows Kirby to gain the initial speed of a slide, while not needing to wait for it to end, as it is cut short once Kirby leaves the ground.

Instant Inhale

If Kirby is close enough to an enemy when initializing an inhale, he will instantly inhale it in his mouth, cutting the inhale animation short. This is significantly faster than doing a standard inhale, as the animation typically needs to start and finish for a set amount of time.

Jet

About Dash State

Most of Jet's moveset is based around whether or not Kirby is dashing. It is important to be mindful of when Kirby should be dashing, including when Kirby leaves the ground.

There are many cases in the speedrun where Kirby will need to leave the ground while dashing, as a specific move is needed which requires Kirby to be in a dashing state.

For example, if Kirby were to use his Jet dash move in the air while in a dash state, he will go much farther than if he were not in dash state. When typically doing Jet Strings, Kirby needs to leave the ground in dash state in order to execute the faster Jet dash.

Wheel

Turn Boosting

If Kirby quickly turns around before leaving Wheel state, he will get a sudden boost of horizontal speed.

This is only possible in standard Wheel form (Wheelie cannot do this). It is used primarily at the beginning of GCO Any%.

Edge Shredding

Wheel can be used to destroy bosses by staying against the edge of the screen.

In order to perform this, Kirby first needs to be approaching the wall in Wheel form. Before hitting the wall, hold B to start breaking. This will prevent Kirby from bonking against the wall. Once Kirby is against the wall, let go of B so that he will not take hit damage.

Wheelie

About Jumping

While Wheelie is airborn, it is important to let go of B as quickly as possible, as having B held will cause Wheelie to take damage.

High Jumps

By dashing, jumping, and using Wheel all in quick succession, Wheelie will have a boosted jump height. This is used in various sections, such as GCO Any% Crystal, where Wheelie would not have the required height to otherwise clear certain jumps.

Plasma