Many special moves, in addition to being unique, are also chargable!
If you release it before it’s fully charged, it will be fairly weak and not too special.
But, if you wait until you’re fully charged?
There are a few things to note about these kinds of attacks:
If you press left or right while charging, you’ll cancel it into a roll. You’ll keep any charge you had accumulated, too.
Once you’re fully charged, there will be an indicator present on your character.
And not all characters can cancel their chargable specials. These attacks must be performed immediately at full charge.
Try out all of the characters! There are plenty of these types of moves to have fun with.