Sonic Battle was a fighting game for the GBA and it came out sometime around spring of 2004.
[SPOIL="Spoilers for those who haven't played Sonic Battle."]The characters in the game are Sonic, Tails, Knuckles, Amy, Cream, Rouge, Shadow, Emerl, E-102 Gamma (unlockable), Chaos (unlockable), and Eggman who is unplayable without cheat codes. Emerl was a robot that Gerald researched. The robot and Shadow were the two ultimate lifeforms, and with each Chaos Emerald found, Emerl would have its speech, and fighting skills improve. Emerl was a machine of destruction if it had all seven Chaos Emeralds and a special link wasn't said, or if Emerl was near a imense amount of energy. Most of the game revolved around Emerl, and at the end of the game, Eggman unlocked Emerl's ultimate power, and Sonic (who had the Master Emerald in his possesion at the time intill Emerl destroys it) had to battle Emerl (who was basically faster than Sonic's or Shadow's top speed, and did the most damage than any other character). At the end of the game, Emerl was destroyed.[/SPOIL]