Super Sonic
From Sonic Retro
Super Sonic, first seen in Sonic 2, is achieved when Sonic collects all seven of the Chaos Emeralds. He has appeared in almost every single main title since.
In the Games
In Sonic 2, Sonic 3, and Sonic & Knuckles, Sonic is capable of achieving this state after collecting all of the Chaos Emeralds, fifty rings, and pressing jump twice (except in Sonic 2, in which he automatically transforms when jumping). In this state, Sonic dons a glowing gold color, and he is virtually invincible, faster, and can jump much higher. There is one catch to this: one ring is lost every second. Sonic can maintain this state with a constant supply of incoming rings, but once he runs out, he will revert back to his normal self. Super Sonic is vulnerable to death via the same methods as his normal form is regardless of whether he has rings, including falling down a bottomless pit, being crushed, or drowning.
First seen in Sonic & Knuckles, it has become a recurring theme for Sonic to transform for the game's final boss. For such bosses, Sonic already starts out with fifty rings, and even though Super Sonic is invincible to all attacks, there have been some cases in which the bosses may find ways to rob Sonic of his rings. Sonic Adventure was the first game to feature Super Sonic playable only in the final boss, and from this point on, Sonic is incapable of transforming in-game. A few notable games to not feature Super Sonic at all are Sonic Battle and Shadow the Hedgehog.
Although Super Sonic's playability these days is mainly restricted to final bosses, there have been few times in which he is fully playable, albeit only in spin-off titles. He is an unlockable character in Sonic Shuffle after the player buys all of Sonic's pictures. His special ability is high-speed movement: when the same number is placed twice in a row, Super Sonic will move twice as far; this can be chained for up to three times.
In the Sonic Riders series, the Chaos Emerald gear is unlocked when the player completes all missions with gold medals (or Extreme rank in the sequel), which only Sonic may use. In races, Sonic starts off with thirty rings which depletes by the second. Although he has infinite air and has all three attributes (Speed, Flight, Power), Super Sonic uses up rings at a much faster rate when drifting, boosting, or attacking opponents. When he runs out of rings, Sonic takes to running on foot until he can collect a single ring. In the sequel, Sonic Riders: Zero Gravity, Sonic starts off with no rings, yet when he does collect them, they deplete at a very slow rate, giving him time to build his supply. As above, Super Sonic's ring total depletes at a multiplied rate when he uses gravity control, making it very impractical to use it at all. Once he collects 60 rings, Super Sonic goes into a permanent boost mode (acquiring the Power attribute, the only one Super Sonic possesses in the game) and his supply runs short quickly.
In the Comics
In the UK comic series by Fleetway, Sonic the Comic, Super Sonic is evil. Under extreme stress or exposure to Chaos Energy, Sonic transforms into a demon-like version of Super Sonic. His abilities from the original games are the same (faster, invincible, etc.), except he can fly and can fire laser blasts from his eyes. He is completely uncontrollable and destroys anything and everything, whether it be because it is in his way or for the fun of it. When Sonic reverts back to himself, he has no recollection of any events that have occurred.
The "Running Wild" multi-part story was a major turning point; as Sonic was accidentally exposed to the Chaos Emeralds and Master Emerald at full power at the same time, he emerged more psychotic than ever before and tried to kill Amy Rose, Tails, and Johnny Lightfoot. They were able to trick Super Sonic and, with the help of a starpost, managed to separate Sonic from Super Sonic, with Super Sonic warped to the Special Zone. In the last few issues of the comic (the "Chaos Saga," an adaption of the game Sonic Adventure), Super Sonic was merged back into Sonic by a comic-exclusive character called Ebony.
Super Sonic is a fan favourite amongst the Sonic the Comic community, as he represents a more dark, edged version compared to Sonic Team's version of him. In a demonstration of the "eye of the beholder" principle, his fans and his detractors often cite the same exact reasons for their opposite opinions.
A single issue of the American Archie comic series actually features an evil Super Sonic. When Sonic is accidentally transported into space, he comes across a colony that possesses a set of red Chaos Emeralds (which strikes Sonic as unusual, as the Chaos Emeralds on his planet were all green). While the colony is under attack by rival aliens, Sonic uses the red Chaos Emeralds in a desperate attempt to save them. However, this causes Super Sonic to separate from him, who wastes no time in laying havoc on the colony himself (including the rival aliens). Sonic manages to hold him off, but is unable to defeat him. However, Super Sonic eventually fades away, as much like the real Super Sonic, his power is only temporary.