Mecha Sonic is the primary antagonist for the first saga of Super Mario Bros. Z. In his original appearances (Episodes 1 - 3), Mecha Sonic was given voice clips of the Ninja Robots from "Mortal Kombat". However, starting with Episode 6, he is given voice clips of Final Form Cooler from the "Dragon Ball Z: Budokai Tenkaichi" series of games (with the exception of his saying "Chaos Blast").
In the beginning prior to SMBZ, Mecha Sonic was born Metal Sonic, as told in episode 4. He was created by Dr. Eggman, after his attempts of destroying Sonic by using robotic models of Sonic failed indistinctly. Sonic fought him countless times, and was defeated. Metal Sonic would return a lot more stronger after each defeat. One night at the Death Egg, things take a turn for the worst, Metal Sonic fuses with the previous robot Sonic models and becomes Turbo Mecha Sonic.
When Dr. Eggman discovers this, he threatens to shut him down for his rebellion. Mecha Sonic goes berserk and destroys the Death Egg, causing it to crash in Mobius. When he gets out of the ruins, he becomes a bloodthirsty mechanical demon with a lust for power. He starts by killing Tails, Amy, Knuckles, Cream and Cheese and the majority of the innocent animals of Mobius, while in search for the Chaos Emeralds. When he defeats Sonic, he takes his Emerald and prepares to turn in his ultimate form, but thanks to Shadow, it is prevented, however he escapes to the Mushroom Kingdom to find the Emeralds.
In Episode 3, he fights and easily defeats Yoshi, however he did not finish him since he felt Sonic's presence in the Mushroom Kingdom. In Episode 6, he defeats the Koopa Bros and steals their Emerald and brutally destroys the Axem Rangers X, after fusing himself with four of the Emeralds becoming Semi-Super Mecha Sonic. He completely destroyed Yoshi's Island, but not before the Emeralds are taken from him by Sonic.
In Episode 7, he assaults Mario and Sonic, but when he is in the Minus World he cannot go on Chaos Control. The heroes escape before he could incinerate them.
More facts are known in future episodes. Alvin has confirmed that he will collect all of the Chaos Emeralds
Mecha Sonic appears to be the strongest character in SMBZ so far. According to Axem Red's scouter, his power level is "over 9000," although the power level of other characters is unknown. What is known is that Mecha Sonic easily defeated Sonic and his friends and is able to match Cape Mario in a one-on-one battle, while handicapped.
Mecha Sonic is incredibly fast and strong and uses martial arts style attacks in battle. He also possesses a machine gun and missile launcher in his arm, although they are not used quite as often. Mecha Sonic also uses energy beams and blasts in battle, the strongest of which must be charged up before use.
Being made out of metal, Mecha Sonic has impressive defenses and can recover from most attacks rather quickly. He also possesses an energy shield reminiscent of the magnetic barriers in Sonic games. The shield allowed Mecha Sonic to survive a blast from an Emerald-powered Breaker Beam, so it is unknown how much power would be required to break or penetrate the shield.
Mecha Sonic is capable of flying at will due to built-in jets and can remain airborn for an unknown length of time (perhaps indefinitely). He can also roll into a ball and spin around in the same manner as Sonic, a technique he uses for attacking, defending, and mobility.
Ever since Sonic Heroes, Mecha Sonic has been able to analyze and copy the abilities of other fighters. So far he has demonstrated Sonic's light speed attack (allowing him to move so fast it seems as though time stands still, although it must be charged before use) and Shadow's Chaos Control and Chaos Blast techniques. It is unknown if Mecha Sonic has yet copied the abilities of anyone from the Mushroom Kingdom.
Although quite powerful unaided (he is shown in Episode 7 to be more than capable of holding his own against and overpowering both Mario and Sonic simultaneously), Mecha Sonic can make himself even stronger by using the Chaos Emeralds. Although he can use all seven Emeralds to enter a Super form, he only needs four to power up. This Semi-Super form greatly increases Mecha Sonic's speed, power and defense, allowing him to survive Axem Red's secret weapon without even flinching and making him even faster than Sonic (he laughed to himself, stating that he was merely toying with the Mario quintet through out the battle). Semi-Super Mecha Sonic also needs less time to charge energy attacks and is capable of stronger energy attacks, including one that can destroy an entire island. Although Mecha Sonic's Super form, Metallix, hasn't yet been seen outside of the saga opening, it would logically be even stronger than his Semi-Super form.
Mecha Sonic is a cruel and cold-hearted killing machine who loves to see people suffer. He also seems to view himself as a god. He views his opponents as being unworthy and do not deserve to have the power of the Chaos Emeralds or unworthy to live.
The thing that sets Mecha Sonic apart from the other Sonic robot models was his persistence. His goal was to do that which he was programmed to do: destroy Sonic though Mecha Sonic does see a threat in Mario as well.