Following the roboticization of Sally Acorn, Dr. Eggman decided to create a team of robots to accompany her on missions, including Metal Knuckles, Metal Tails and a new model of Metal Sonic. The team's first mission was to track down the traitor Snively Robotnik, who fled to the United Federation. Mecha Sally and Metal Sonic were sent to distract G.U.N.'s forces-including E-123 Omega- so Dr. Eggman could find the treacherous Snively. After an ensuing battle Mecha Sally and Metal Sonic were called back by order of Dr. Eggman. (SU: #37, #38)
Debut of Team Metal
Three of the Metal Series Units-Metal Sonic, Metal Tails, and new addition Metal Amy-were sent to New Mobotropolis to destroy Team Freedom so Dr. Eggman could conquer the city with ease. However,the group christened Team Metal was destroyed by Team Freedom with a little unseen help from the Secret Freedom Fighters. (StH: #240)
Invasion of Albion
Metal Knuckles accompanied Lien-Da and the rest of the New Megaopolis Dark Egg Legion to Albion to assist in the subjugation of the surviving Echidnas there. When Team Fighters arrived, Metal Knuckles quickly attacked them, while he easily beat Sonic and damaged the Tornado, he was quickly swatted away by Amy's hammer. Later, when Team Fighters assaulted the base, Metal Knuckles appeared again to support and apparently knocked Sonic out. In reality, the battle continued until a defense system rendered everyone unconscious, and Metal Knuckles was taken offline. Unfortunately, the robot Echidna became a new host for the Krudzu as a result. It would eventually be defeated in battle by Team Fighters and Shard the Metal Sonic, who had participated in Team Metal's destruction. (StH: #243, #244, #245, #246)
Old VS. New
Dr. Robotnik had a series of Metal Sonics simlar, but inferior to the one seen in the Metal Series. He was later rebuilt by Sir Charles Hedgehog and renamed Shard to be a member of the Secret Freedom Fighters. (StH: #25, #86, #87, #238, SU: #41, #43, KCX)
Sir Charles Hedgehog and Rotor built an army of Metal Sonic Troopers to defend Knothole against Dr.Eggman when Sonic was believed to dead. They were created from technology reversed engineered from the original Metal Sonic. (StH: #157, #158, #159, #238)
Dr. Eggman's first six versions of Metal Sonic were all identical to the latest Metal Sonic, but with varing levels of strength and abilitys in comparrison.(StH: #146, #147, #148, #149, #157, #191, #192, #195, #196, #230, #234) (FCS: #1) (SX: #40) (SU: #1)
Dr. Eggman created a series of Silver Sonics called Silver Sonic II and Silver Sonic III, the former to attack Station Square and the latter to protect the Death Egg Mark 2. One Silver Sonic III was also deployed against Furville under Mecha Sally's command. (StH: #82, #85, #98, #225, #230, #231, 239)
Dr. Eggman created a robot duplicate of Scourge called Metal Scourge to assist Metal Sonic in defeating Sonic and Scourge. His design is identical to Metal Sonic, but is green in color and wears a leather jacket just like the one Scourage wears. (StH: #191, #192)
Dr. Eggman built a giant version of Metal Sonic called Titan Metal Sonic to destroy New Mobotropolis as a diversion to allow the damage Death Egg Mark 2 and his forces to retreat. A second Titan Metal Sonic was later employed against Team Fighters after being combined with the Krudzu Hybrid Hydra. (StH: #231, StH: #241)
Each Metal series unit has abilities similar to it's organic counterpart such as Metal Sonic having similar abilities to the real Sonic. However, each unit also has enhanced strength due to their robotic nature, and all are equipped with engines to allow them to fly. Members of the series have also been shown to be equipped with weaponry, ranging from blades and hammers to laser cannons.
- The Metal Series could be based off Marvel Comics The Enforcers due to Dr. Eggman anouncing his New Enforcers. The characters even stand close to each other and strike poses similar to Marvel Comics The Enforcers.