Neo Metal Sonic

Neo Metal Sonic (ネオメタルソニック) is one of Metal Sonic's transformations seen in Sonic Heroes. He takes this form throughout most of the game in which he uses to disguise himself as Dr. Eggman and to copy the data of whom he fought against in order to make himself more powerful.

Appearance
Neo Metal Sonic shares some distinctive traits with his normal form, such as black eyes with red irises, similar torso with rocket engine and the primary blue color with red shoes, but has number of differences too. His head has five long quills as opposed to his regular three, with white stripes and markings around his eyes, similar to that of Shadow's. The yellow color in his ears has been replaced with red and his nose is now black.

He has also possess more pronounced body armor, with black and curved shoulder plates, larger gauntlets and leg armor with pointy knee caps that has white outlines, a plate covering his pelvis and elf-like shoes. He also sports a spiky belt with a black cape that protrudes out of the back of his waist.

History
Under unknown circumstances, Metal Sonic assumed this form as a result of his several losses to Sonic the Hedgehog. Consequently, the metallic hedgehog decided to defeat Sonic on his own and conquer the world himself. To this end, Metal Sonic betrayed Dr. Eggman, took control of the Eggman Empire and began seeking out the data needed for him to transform into Metal Overlord. Somewhere around this time, Metal Sonic assumed the form of Neo Metal Sonic.

To get the data he needed, Neo Metal Sonic elaborated a plan where he would send Team Sonic on a wild goose-chase to destroy "Dr. Eggman's" newest weapon. Then, by using his form's shapeshift-abilities, Neo Metal Sonic masqueraded as a robotic Dr. Eggman and fought Team Sonic on various occasions while copying their data without them knowing. At some point, Neo Metal Sonic used his shapeshifting abilities to pass as the real Sonic, and kidnapped Froggy and Chocola in order to obtain their data on Chaos.

While Neo Metal Sonic only intended to involve Team Sonic, Team Rose, Team Dark, and Team Chaotix entered the conflict as well. This proved however to work in the favor of Neo Metal Sonic, as he continuously faced the teams while masquerading as Dr. Eggman, and began copying their data as well, making himself even more powerful than he planned to.

At the time Team Sonic and Team Dark defeated the Egg Albatross, Neo Metal Sonic had successfully copied Team Sonic's and Shadow's data, and when Team Rose defeated Neo Metal Sonic in the Egg Emperor, he had copied Chaos' data as well, making him release Froggy and Chocola from captivity.

With all the data he needed, Neo Metal Sonic revealed himself to the heroes and destroyed the Final Fortress' tower before using the debris to transform into Metal Madness and later Metal Overlord. However, he was later defeated by Team Super Sonic and reverted to Neo Metal Sonic, and then back to his original form.

Powers and abilities
Neo Metal Sonic is, like his normal form, able to scan the life data of other life forms, allowing him to copy and replicate others' attributes and abilities flawlessly. Due to his actions throughout Sonic Heroes, it can be assumed that, by the beginning of the last story in the game, he possessed the abilities of all the teams, plus those of Chaos itself.

Neo Metal Sonic has the power to shapeshift, allowing him to change his appearance and body structure. When shapeshifting, he turns into a puddle of liquid metal and then emerges in a new form. This allows him not only to perfectly imitate the appearance of organic creatures, but also the appearance of robots as well, such as fake Dr. Eggman robot copies, though Tails could tell it was not an Eggman robot. He can also safely contain creatures such as Froggy and Chocola inside of himself until he had copied Chaos' data.

As demonstrated when he first revealed himself, Neo Metal Sonic can create lightning bolts from his hands, launch them into the sky and then bring it back down with enough power to blow up the Final Fortress' largest tower. He can also manipulate outside elements through unknown means to rebuild himself, such as when he used the debris from the Final Fortress' tower to rebuild himself into Metal Madness.

Metal Madness
By combining the data from Team Sonic, Team Dark, Team Rose and Team Chaotix with the data from Chaos, Neo Metal Sonic is able to rebuild himself into a much stronger form called Metal Madness. In this form, Neo Metal Sonic's strength and power are highly increased and he gains new abilities and weaponry, such as launching the spines on his back which will sprout into a sharp spike formation, a large flamethrower, missiles which can trap his enemies in crystal cages, and a powerful sweep with his tail.

Neo Metal Sonic briefly assumed this form when he tried to transform into Metal Overlord. During this time, he fought Team Rose, Team Dark and Team Chaotix, before he finally transformed in Metal Overlord.

Metal Overlord
After completing his transformation as Metal Madness, Metal Madness grows a pair of mechanical wings on his lower body, becoming Metal Overlord. In this form, Metal Overlord is nearly invulnerable and is powerful enough to fight on par with Super Sonic, Super Knuckles and Super Tails. He is capable of flight and is strong enough to throw entire battleships. As Metal Overlord, he can fire a barrage of crystal pillars from his torso, launch the spikes on his back as homing missiles, fire crystal encagíng missiles, and perform Chaos Control.

After Metal Overlord had finished his transformation, he flew into the skies, but was pursued by Team Super Sonic. Despite his overwhelming power Metal Overlord was defeated by Team Super Sonic and reverted to Neo Metal Sonic, and then his original form.

Archie Comics
In the Sonic the Hedgehog comic book series and its spin-offs, published by Archie Comics, an army of Neo Metal Sonic robots, called the Metal Sonic Troops, appeared. These robots were created by Sir Charles Hedgehog and Rotor to serve as protectors of Knothole after Sonic was lost in the battle with the Xorda. While they were never activated by their creators when Sonic returned, A.D.A.M. managed to assume control of them and send them on a rampage against Knothole and Dr. Eggman. The entire army was destroyed however, when Shadow the Hedgehog used Chaos Control.

After the Super Genesis Wave, just like in the games, Neo Metal Sonic was an alternate form of Metal Sonic, assumed after usurping control of the Eggman Empire from its creator.

Trivia

 * In Sonic Heroes, in Hang Castle, when the player looks at the Eggman statue upside-down, they can see Neo Metal Sonic. This hints at his role in the game.
 * Another hint is in Team Dark's Egg Hawk level. When "Eggman" saw Omega, he said, "You must be Omega...".
 * Another hint is when Team Chaotix is about to fight the Robot Storm, Vector refers to "Eggman" as a "mustached moron", their "mysterious client" becomes enraged and says "I'm the world's greatest..." before catching himself and telling the Chaotix to defeat him.
 * Neo Metal Sonic's designer, Kazuyuki Hoshino, was the one designed the original Metal Sonic.
 * It is unknown how Metal Sonic achieved his Neo Metal Sonic form. It is still possible that Eggman has upgraded him to this form, as Eggman knew of his ability to become Metal Madness because after Neo Metal Sonic's change into Metal Madness, he said, "Metal Sonic has finally transformed!"
 * The only game that featured Neo Metal Sonic's name was Sonic Rivals. He was a collectible card.
 * Despite Neo Metal Sonic's large role (albeit behind the scenes) in Sonic Heroes, the player never actually fights him in this form.
 * Neo Metal Sonic's shapeshifting ability is similar to the liquid-metal shapeshifting ability of the T-1000 from Terminator 2: Judgement Day.