Mecha Sonic (メカソニック Meka Sonikku?) is a powerful robot built by Doctor Eggman that appeared in the game Sonic & Knuckles. He attacks both Sonic the Hedgehog and 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.
Mecha Sonic first appears as an enemy of Sonic (and possibly Tails, if playing Sonic 3 & Knuckles). He appears three times. In the first two appearances, he is piloting Doctor Eggman's Egg 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 power himself up into an invincible, glowing, golden form (referred to as Super Mecha Sonic, after his resemblance to Super 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.
Bulky, mechanized Sonic-clone with few different attack patterns. Takes 8 hits to defeat.
At the end of Sonic's version of Sky Sanctuary Zone, Mecha Sonic is the end boss of the zone without any Eggmobile add-ons in it's previous attempts at the zone. The battle in Sonic's story takes place to the wide arena, that is next to a tall tower by using Warp Point below the arena. After transporting to the arena, Mecha Sonic dashes to arena while destroying the Warp Point from the arena, as the player has to defeat mechanized robot on the way in order to reach to the Death Egg. When Mecha Sonic reveals himself at the end of Knuckles' story, it destroys Egg Robo and is ready to face echidna himself while Angel Island is seen to get slowly sway down at 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 first attack pattern, Mecha Sonic starts off by jumping medium high from the corner to center of the arena, will do it's variation of Spin Attack to the left corner from up and then becomes back to it's idle standing for moment. In the second one, it jumps and dashes from the corner and lands to the other corner to it's standing mode. During the third pattern, Mecha Sonic does a small leap to the arena's center on it's spiky ball mode before doing larger leap, that reaches to the other corner. After that, it spins in mid-air for second before it lands to it's standing mode for 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 the some of patterns, becuase after landing to the corner, Mecha Sonic suddenly starts squat down and do backward dashing to the other corner and there it returns to it's standing mode. The only moment when the player is able to hit Mecha Sonic is when it is on it's standing mode without doing nothing for few moments or when it is doing it's squat dash. During both fights Mecha Sonic takes 8 hits to defeat as after that it kneels down after getting to fault mode.
This robot was not named in the English-language manuals accompanying Sonic & Knuckles, but 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-language 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.
- 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 similiar to Sonic's modern design, except being somewhat purple and inorganic.