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 opponents upward, also able to break through shields. 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 does not appear to have any specific origins, although 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 tried to tame it. This form, often referred to as "Nine-Tails Chakra Mode", greatly enhances Naruto's physical abilities, which are enhanced even further when using Kurama's chakra, making him the most powerful ninja in the Naruto franchise along with 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 (大玉螺旋丸), also known as Big Ball Rasengan, which is an augmented version of Rasengan. It utilizes the concept of compressing spinning chakra in one's palm, just like the original Rasengan, only increasing the amount of chakra involved. Since 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.

Trivia

 * Prior to Beta 1.2, Naruto's Final Smash was instead a Transformation Final Smash, called Kyūbi Naruto.
 * It resembles Robin's Pair up Final Smash in terms of the attacking animation from the official games.