Rosalina uses a Launch Star to propel herself through the air. In addition to covering considerable distance at quite a fast speed, the move can also be angled; holding the control stick backward angles it directly upward, holding the control stick forward angles it at an acute angle and not holding the control stick angles it upward at a slight angle.
Despite its positives, Launch Star has no hitbox and thus has no offensive use whatsoever. It is also susceptible to gimping if the opponent is quick enough and reads the launching angle properly. Lastly, it is also difficult to sweetspot the ledge with, due to Rosalina's large hurtbox and the difficulty in angling her trajectory when facing backwards. However, Luma can still perform aerials while Rosalina is in her helpless state, so Rosalina is not completely defenseless after using this move.
Special Move customization was added in Super Smash Bros. 4. These are the variations:
Launch Stars are a major means of traversing through each planet in Super Mario Galaxy and its sequel. They usually form after clearing an objective needed for each planet, which include but are not limited to freeing a yellow Luma or the Launch Star itself, collecting five pieces called Star Chips, or defeating all of the enemies in an area. They usually come in orange, but they can be pink (leading to a galaxy or planet formed from feeding a Hungry Luma) or green (leading to or found in the Planet of Trials in Super Mario Galaxy). However, none of the stars seen in the games resemble the one used by Rosalina, and the move's Japanese name does not correspond with the respective name of Launch Stars (スターリング, Star Ring).