Mephiles the Dark

 Mephiles, sometimes known as  Mephiles the Dark in other media, is a spirit who took the shape of Shadow the Hedgehog. He is the power and intelligence of the god Solaris. He later became an entity known as the Time Eater.

Plot to Rule Time
Mephiles was a smokey spirit born during an experiment when Solaris, the god of time, light, and fire, was split into two halves- Mephiles, who consisted of power and intelligence, and Iblis, who consisted of Solaris's fiery power and destructive nature. He was trapped within a device called the Sceptor of Darkness by Shadow the Hedgehog. Years later, Mephiles was released and stole Shadow's shape and abilities by merging with his shadow. Cruel and brilliant, he created a plan that spanned over two hundred years, brought him the seven Chaos Emeralds, saw the death of Sonic the Hedgehog and the release of Iblis, who was sealed within Princess Elise. With the power of the Chaos Emeralds, Mephiles rejoined Iblis and Solaris was reborn. His existence was ultimately erased when a resurrected Sonic and Elise traveled back in time to the days before Solaris was experimented upon and snuffed the tiny white flame. Though (according to the Encyclopeia) he may have slipped through a crack in time. (CSE)

Time Eater
What was left of Mephiles slipped through a crack in time and became a shadowy being known as the Time Eater.

The Time Eater had been brought into existence on Mobius Prime after the dimension had its timeline altered by Dr. Eggman and Dr. Wily's Genesis Wave. However, the Time Eater was stopped by Sonic at some point in this new reality's past. Dr. Light later brought up the Time Eater to Eggman in an attempt to state Eggman's experiences about tampering with forces that he could not control. (WC #9)

Zone Jail
Mephiles (or an alternate version of him) was captured and imprisoned in the Zone Jail by the Zone Cops for presumably the same crimes he (or his counterpart) had committed. Unlike previously, this Mephiles was more laid back like Sonic and had incorporated words such as "Dude" into his vocabulary. He was seen hanging out with a fellow universe-annihilating prisoner named Void in the food court when the Destructix saved an ungrateful Scourge from a group of prisoners and asked Void what Scourge's problem was though he was never given an answer. Later, during a massive prison break, Mephiles was seen sliding down a pole as he made his escape alongside other prisoners like the ultra-powerful Robolactus and Anti Cream, but was presumably recaptured when Zobotnik brought in as many reinforcements as he could and has since continued his daily routine. (SU: #29, #32)

Background Information

 * Sonic the Hedgehog (2006) was originally confirmed to happen in the Archieverse in an Ask Ian. Later, in The Complete Sonic Comic Encyclopedia, the plot details were explained.
 * Mephiles is the first Sonic character to actually kill Sonic, however these events were erased from history.
 * Mephiles is one of the SegaSonic characters who are off-limits, as confirmed by Ian Flynn.
 * According to Ian Flynn on the Bumbleking forums, the Time Eater is implied to be leftover matter of Mephiles that somehow managed to "slip through a crack in time". This could explain its purple aura and similar ability to travel through time.