Mecha Sonic (Sky Sanctuary Zone)

Mecha Sonic (メカソニック) is a powerful robot built by Doctor Eggman that appeared in the game Sonic & Knuckles. He attacks either Sonic the Hedgehog or Knuckles the Echidna, and appears in the Sky Sanctuary Zone in five separate boss battles across the two story lines of the game (three times against Sonic and twice against Knuckles). He can roll into a ball and spin-dash just like his living counterpart. He can also float as a spiky ball and attack from above.

History
Mecha Sonic first appears as an enemy of Sonic (and/or Tails, if playing Sonic the Hedgehog 3 & Knuckles). He appears three times. In the first two appearances, he is piloting Eggman's Mobile, first with an attached checker-ball weight (as Eggman did in the Green Hill Zone in Sonic the Hedgehog) then surrounded by swirling orbs (as Eggman did in the Metropolis Zone in Sonic the Hedgehog 2). In his third and last battle against Sonic, he now appears on foot, and the two fight hand-to-hand.

Although Sonic defeats his Mecha counterpart, the robot is shown to survive the battle. He reappears in Knuckles' story as the final boss of the game. First, Knuckles defeats him in a simple one-on-one fight (as Sonic did). Then Mecha Sonic flees to the Master Emerald, which he uses to initiate a super transformation into "Super Mecha Sonic". In this form he is untouchable, and does damage to whoever touches it but Knuckles is able to defeat him by striking when his power runs out and he is forced to go back to the Master Emerald for a short recharge. When Knuckles defeats the robot this time, he explodes, this time defeated for good. However, his destruction also takes the remains of the Sky Sanctuary with him, Knuckles only barely escaping with Sonic's help, the latter piloting the Tornado.

Battle
At the end of Sonic's version of Sky Sanctuary Zone, Mecha Sonic is the end boss of the zone without any Eggman Mobile add-ons in its previous attempts within the zone. The battle in Sonic's story takes place in a wide arena, that is next to a tall tower by using a Warp Point below the arena. After transporting to the arena, Mecha Sonic dashes across the arena while destroying the Warp Point to the arena, as the player has to defeat the mechanized robot in order to reach to the Death Egg. When Mecha Sonic reveals himself at the end of Knuckles' story, it destroys Eggrobo and is ready to face the echidna himself while the Floating Island is seen to slowly sway down in the background. Battles on both stories are identical.

Mecha Sonic is known to have different attack patterns, which are loosely similar to previous Mecha Sonic's attack movements from Death Egg Zone of Sonic the Hedgehog 2. In its first attack pattern, Mecha Sonic starts off by jumping medium high from the corner to the center of the arena, will do its variation of the Spin Attack to the left corner from above and then returns back to its idle standing position for the moment. In the second one, it jumps and dashes from the corner and lands in the other corner, assuming its standing mode. During the third pattern, Mecha Sonic does a small leap to the arena's center on its spiky ball mode before doing a larger leap that reaches to the other corner. After that, it spins in mid-air for second before it lands to its standing mode for a few seconds. The last pattern features Mecha Sonic floating and then dashing through the air directly to other corner.

However, the player has to watch out the last moment on some of the patterns, because after landing in the corner, Mecha Sonic may squat down and dash backward to the other corner before standing upright, attempting to poke the player with it's spines as it dashes backwards. The only moment when the player is able to hit Mecha Sonic is when it is standing upright. During both fights, Mecha Sonic takes 8 hits to defeat as after that it kneels down and starts to short circuit as electricity crackles across its body.

Naming
This robot was not named in the English-language manuals accompanying Sonic & Knuckles, but the description on the back of the box erroneously refers to him as "Metal Sonic". In the Japanese strategy guide, he was called "Mecha Sonic" (as were the Sonic robots in both versions of Sonic the Hedgehog 2). He was also called "Mecha Sonic" in the Japanese official strategy guide for Sonic Jam.

"Mecha Sonic" was confirmed as his official English name in the backstory for Sonic the Hedgehog 4: Episode I, released in the Story section of the official English website, implying that this Mecha Sonic is directly rebuilt from Sonic the Hedgehog 2.

Sonic the Comic
A Metallix robot based on Mecha Sonic appeared in Sonic the Comic's adaptation of Sonic & Knuckles. He stole the Master Emerald from the Hidden Palace Zone and was followed by Sonic and Knuckles to the Sky Sanctuary Zone. As in the game, he super-charged himself with the Master Emerald's energy, becoming invincible. However, he was defeated by Super Sonic when Sonic tried the same trick.

Trivia

 * Mecha Sonic is the first villain to manage to achieve a Super State, the first inorganic character to ever use a Super State (the other being Gemerl at the end of Sonic Advance 3), and the very first overall to trigger a transformation by use of the Master Emerald (the next would be Pir'Oth Ix, over a decade later).
 * He is also the only character with a Super State that does not last long, forcing him to retreat to the Master Emerald for another charge up. The second half of the battle displays him remaining in his Super State and no longer needing the Master Emerald to maintain it, though he is seen periodically reverting back to his normal form and then quickly powering up afterwards, hinting that his Super State is also the only Super State that is not stable.
 * The first phase of Mecha Sonic's battle theme during Knuckles's playthrough is the same as the battle with Eggman on the Death Egg, and the second phase is the same as the Doomsday Zone.
 * Mecha Sonic's fate in Knuckles's story depends on whether or not the player has collected all of the Chaos Emeralds (or Super Emeralds if playing Sonic the Hedgehog 3 & Knuckles). If the Emeralds aren't collected, then Knuckles will lose the Master Emerald, and Mecha Sonic will reactivate with the Master Emerald in his possession again. If all Emeralds are collected, then Mecha Sonic will be last seen breaking apart and Knuckles will reclaim the Master Emerald.
 * Mecha Sonic seems to be very similar to Sonic's modern design, except being somewhat purple and inorganic.