You're probably more interested in learning about a technique called 'break boosting'. I'll give you a brief introduction to it.
In short, how you do it is
1) run in place briefly (less than 0.5 seconds, typically less than 0.1 seconds)
2) spin dash
3) quickly let go of your directional input (analogue or d-pad) (aka neutral sliding)
at this point if you've done it right you can spontaneously gain speed
4) (optional) tap down for another boost and then jump as close to tapping down as possible to prevent losing speed from friction
~ The Different Variations of Break Boosting ~
I'm going to assign some names here though I think for the most part this is what these are generally refereed to as.
- (Normal) Break Boosting - This is quite often done at the start of levels before you even move at all. Kick the level off with extra speed. This is also done later in the level, often prefaced with a down smash to halt your momentum. Once you're stopped it operates exactly the same.
- Wind Boosting (aka DAT WIND) - Break boost in upward drafts of wind. It highly amplifies the affect of break boosting. (horizontal wind is also good but I don't recall it being quite as good as upward wind)
- Skid Boosting - Instead of completely stopping with a down smash, you can let friction stop you while neutral sliding (not pressing a direction but letting momentum push you along). You can then break boost after being stopped for a few frames (1 frame = 1/60th of a second). This can be faster than down smashing to set up a break boost in some applications because of the amount of time it takes to perform those tasks. Its a very obscure break boost but can definitely be useful.
This is the DUMBEST way I've ever seen to gain speed. | Ubisoft Forums