Tailed Beast Rush

Tailed Beast Rush is 's Final Smash in Super Smash Flash 2.

Overview
When performed, Naruto summons a Shadow Clone in front of him that kicks upward. Opponents hit by this kick are dealt 5% damage and launched into the air as Naruto and his Shadow Clone both enter their Nine-Tails Chakra Mode and jump towards them. They then deliver a series of punches and kicks on the opponents dealing 35% damage, total. Afterward, the opponents start to fall, and Naruto and his Shadow Clone fall towards them to unleash an Ōdama Rasengan together that deals 13% damage and powerful knockback to opponents hit. Upon landing, Naruto returns to his normal form and the Shadow Clone disappears, ending the move.

Origin
Tailed Beast Rush doesn't appear to have any specific origins, though it does feature Naruto's Nine-Tails Chakra Mode, which he uses in the later parts of Naruto Shippūden. Specifically, it is based on the second version of the form, which Naruto learns after he befriends Kurama, the tailed beast sealed within him, while in the first version Naruto just defeated the beast and force it to provide him power. This form, often referred to as "Kurama Mode", greatly enhances Naruto's physical abilities, which are enhanced even further when using Kurama's chakra, make him the most powerful fighter still alive in his universe, along with his best friend and ally Sasuke Uchiha. It also covers his body in yellow chakra from which he can create chakra arms, which Naruto generally uses to form the Rasengan without the aid of his Shadow Clones, though this is not present in SSF2.

The Final Smash also includes the Ōdama Rasengan, also known as Big Ball Rasengan. It is the augmented version of Rasengan, along with Rasenshuriken. It uses the same concept of compressing spinning chakra in one's palm as in the original Rasengan, only increasing the amount of chakra involved. Because there is even more chakra being compressed to a higher density, the ball releases its energy immediately on contact, thus increasing its destructive power beyond the Rasengan's. Compared to its counterpart Rasenshuriken, the Ōdama Rasengan has less mobility and range, but more intensive power. This means the technique is best used in melee range, as seen in SSF2, where Naruto rushes downward towards his falling opponent as a finishing move.

Trivia

 * Prior to Beta 1.2, Naruto's Final Smash was instead a Transformation Final Smash, called Kyūbi Naruto.