In the attack, Sonic uses the power of the seven Chaos Emeralds to transform into Super Sonic that is able to fly quickly and attack fighters by ramming into them.
The screen zooms in on Sonic, and he transforms, based on the transformation animation from Sonic the Hedgehog 2. When Sonic transforms, he gains the ability to fly around the stage at an incredible speed. The transformation lasts for about 15 seconds (though this can be extended by ramming into opponents and other things that can take damage, causing him to freeze for a moment), and is completely invincible for its duration. He is also unaffected by Bumpers. Sonic can attack in this form by simply ramming into opponents; the faster he is going, the more damage he deals. When the opponent is attacked, the move deals about 35%, but the first attack is roughly 25%, and never lower (the attacks are variable in function of this speed: 12%/19% in SSB4). It is similar in function to Pikachu's Final Smash, Volt Tackle, except that it cannot go through hard platforms like Volt Tackle can (however, when Sonic is too slow or has stopped moving, he will be unable to go through soft platforms), and has better knockback and control. Super Sonic cannot KO himself when he reaches the blast line, regardless of how far it is going, but if he turns back to normal while he is too far away to recover, he will be penalized with a self-destruct.
Sonic's Final Smash is arguably among the strongest in Brawl, as the player cannot take damage for its entire duration, and cannot be KO'd, unlike other transformations such as Wario-Man and Giga Bowser. Furthermore, an experienced player who has learned how to control Super Sonic's unwieldy movement can use his high damage output, knockback, and speed to guarantee multiple KOs. Even then, he can fly around a single target and rapidly rack up damage in a focused vicinity, making him hard to avoid.
Super Sonic's attack power was weakened drastically in SSB4, though it is still a potent Final Smash.
Upon activating the Final Smash, Sonic says "Now I'll show you!" in the English version of Brawl. In English versions of SSB4 and Ultimate, this is replaced with "Super Sonic style!", a snippet recycled from Sonic Generations. In the Japanese version of each game, he says "決めてやる!" (I'm going to settle this!).
The Final Smash returns in Ultimate largely unchanged in principle, but with one major alteration: the player has no control over his horizontal movement for the duration. He instead flies back and forth across the screen automatically (with even greater speed compared to the previous games), while the player can only control his vertical position. Overall, the move lasts for a much shorter duration, and can often be avoided completely by crouching. Contact with Super Sonic inflicts 6% damage for each impact and weak vertical knockback, however towards the end of the move, the knockback of each hit is increased, and the ending hitbox deals 10% damage and fairly strong vertical knockback.
How fast Sonic flies back and forth between the edges of the screen depends on the stage's camera view. On stages similar to the size of The Great Cave Offensive, he flies slowly, while on a stage with a camera view similar to 3D Land, he flies very rapidly between the screen's edges, and the attack will often prove fatal to at least one opponent if used correctly.
Sonic's Final Smash. The Chaos Emeralds give energy to all living things, and Sonic's gathered all seven of them, then used their power to transform into Super Sonic. His abilities in this form far surpass his normal ones, and he is even able to fly. He uses a lot of energy in this form, so he can only remain in it for a short time.
The Chaos Emeralds are said to hold enough power to control the whole world. It's that power that turns Sonic into Super Sonic. He turns a glorious golden color and can fly at nearly the speed of light. In his Final Smash, this high-speed flight damages anyone who gets in its way and can even launch them!
In the Final Smash, the Chaos Emeralds appear briefly before Sonic turns into Super Sonic, and once he transforms back into Sonic. In the latter instance, the Chaos Emeralds fly off the screen in 3D.
Throughout the series, Sonic has to collect all seven Chaos Emeralds, usually hidden within Special Stages, in order to turn into Super Sonic, a temporary form that grants Sonic invincibility and increased speed, accompanied with flight in some instances. However, the Super form is still vulnerable to instant death hazards, such as bottomless pits, crushing or drowning. At least 50 rings are needed for the transformation to occur, which will normally drain one ring per second while active and will be reverted as soon as the user is depleted of rings. Starting with Sonic & Knuckles, the Super form is often required to fight against the final boss, and starting with Sonic Adventure, the Super form is usually only available during this fight or made available during regular levels after defeating the final boss.
In Ultimate, the transformation gives the stage a back drop resembling a dark void, similarly to where several final boss fights in the series take place, such as those against Solaris, Alf Layla wa-Lyla, the Dark Queen, the Time Eater, and the Phantom King.