Dark Sonic

Dark Sonic is a dark super transformation achieved by Sonic the Hedgehog in the anime series Sonic X. The multitude of fake Chaos Emeralds and Sonic's intense anger due to seeing cosmo being scared allowing him to achieve this transformation.

Appearance
Dark Sonic seems to have two forms. During his mid-transformation, he still appears like Sonic but his fur is a dark blue color and has a dark blue aura emitting from his body. In the final phase of his transformation (his full transformation) however, he looks similar to Super Sonic (thus the reason why he is also called Dark Super Sonic), and his back quills are longer, similar to Nazo. He still retains the dark blue aura around him but his eyes have no pupils or irises, his fur is black and his skin is a dark grey color.

History
When Sonic first crashes into the Metarex's base in episode 67, after seeing how many fake emeralds there are, he feels uneasy. These comments are prompted by the negative energy Sonic can feel from the fake emeralds. It is this dark chaos energy that incredibly intensifies Sonic's rage at seeing an unconscious Chris and a terrified Cosmo trapped, that causes him to turn into Dark Sonic in his mid-transfomation form.

Black Narcissus then dispatched two robots, Gold and Silver, that he designed to test Sonic's strength and speed. Dark Sonic seems to take a murderous pleasure in doing so, indicated by his mad cackling and evil grin beforehand and quickly tore them apart which then shows him in is full transformation form. Just then, Doctor Eggman turns up, who declares he has never seen Sonic so worked up before. Eggman says he does not want to see Sonic act out of anger and rage and how it is not good for him as Sonic powers down to his normal self.

Powers and abilities
As Dark Sonic, Sonic demonstrates light-speed movements, high enough to tear through a robot multiple times within a second simply by dashing through it, while not even being visible. He also possesses very high physical strength, enough to make dents in metal and caves in a robot's face with one punch, and tear a robot vertically in half with one swift strike.

Personality
Dark Sonic seems to relish the prospect of murdering the two prototype Metarex, as shown by his demonic grin and mad cackle. In this form, Sonic's rage is out of control and he has even gained the intention to kill. However, he can still control his actions to an extent, as this form is rooted in the darker aspects of Sonic's natural instincts, including the desire to live, trample and impose over opposition, and on a metaphysical level, the natural occurrence and manifestation of loss, decline, destruction and death.

Trivia

 * This transformation was initially not given an official name. It was most commonly called "Dark Sonic", which may have inspired its official designation. Due to its similar appearance to Super Sonic, some fans also use the name "Dark Super Sonic."
 * Surprisingly in 2016, Sega named this transformation as Dark Sonic, whereas TMS Entertainment (in 2020) named this transformation as Dark Super Sonic, officializing the name basically.
 * When Sonic transforms into Dark Sonic, his voice sounds slightly lower, similar to Sonic the Werehog.
 * When Dark Sonic shows his face for the first time, music that sounds like the Sonic X theme for Shadow the Hedgehog plays shortly before Dark Sonic takes off into battle.
 * Despite only appearing in one episode, Dark Sonic is one of the most popular characters in the series being included in fanart, fan movies, fanfiction, etc. Fans have asked about the possibility of his inclusion in the Archie Comics, but Ian Flynn has stated that he does not consider Dark Sonic a true transformation.