After yet, another defeat by the hands of Sonic, Dr. Robotnik decided to rebuild Eggrobo and send him out to search for the Chaos Emeralds, as Eggrobo was searching he found and kidnapped Tails hoping to lure the blue blur out.
Tails had other plans, and proceeded to escape to Robotnik's Base without being noticed Tails managed to steal spare robot parts Robotnik had and quickly left, with Sonic nowhere to be found Tails built his own take on Metal Sonic's classic model Codenamed: METAL.
This version of Metal Sonic had the Ability to think and feel similarly to Sonic, after completing the project Tails tracked Eggrobo's last location to Robotic Isle, he then sends Metal Sonic out to put a stop to Eggrobo and Eggman's Plans.