The second key role of the fireball is as a setup. A well placed fireball acts as a surrogate; an intermediary. Its an obstacle. It sets up an initial challenge that must be overcome before you have any chance to actually deal out damage to the opponent. Dealing with it can be as simple (or as hard) as avoiding it (jumping, ducking, canceling it, invincible special, etc.), but it must be dealt with, because its directly threatening you. Whether it hits, or even if blocked, its going to do damage, as well as pushing you around. It must be dealt with because it stands between you and your opponent, and no matter the beating it takes, hurting it wont alone doesnt affect him. Once away, a fireballs fate is entirely distinct from your own. This type of threat can prompt your opponent to take put themselves in more vulnerable positions (like trying to jump over it, etc.), so its a setup in that way, but in some cases, it can also be followed in, like a kind of shield (or jumped over, used to cross-up, etc.), making all sorts of otherwise untenable attack approaches possible. Its an ally that works independently.
