Carl "Mecha Sonic" Robotnik

Carl, more commonly known as Mecha Sonic, is an antagonist in the Sonic the Hedgehog series. In Sonic Vs. Garfield: Battle for Syria, he is an antagonist in both Sonic and Garfield's stories, but a playable campaign with him and Kirby as main characters can be unlocked. In the same game, Other versions of Carl can be fought in the Battle Tower as boss encounters. Despite his rivalry with Sonic, the 2 are able to work together if a greater threat is at hand. As mentioned earlier, there are multiple co-existing versions of Carl, but it is implied they all share the same memories and programming.

Sonic the Hedgehog 2 (SEGA Master System/Game Gear)/Sonic Mania (MK1)
This was the earliest appearance of the robot, and therefore his first design. This version of the robot is named Carl MK1 in Sonic vs. Garfield. This design resembled Sonic in shape and size, but lacked ears and was white in color with a yellow muzzle and chest as opposed to Sonic's flesh tone in those areas. Instead of having eyes that resembled Sonic's, his eyes looked more like blue goggles with a red "eye". His chest was able to open and sent out an extending claw to make up for a lack of proper arms, though in more recent depictions this is omitted in favor of having the arms be said claws. His shoes are also Blue in color and have rocket attachments that allow him to go at higher speeds. Several smaller duplicates appear during Meta Sonic's fight in Sonic Mania.

Sonic the Hedgehog 2 (SEGA Genesis)/Sonic Pocket Adventure (MK2)
Known as Carl MK2, this design is fought in Death Egg Zone and on Eggman's Aerobase. This is also the version that is playable in Sonic Vs. Garfield. This design is silver in color and is larger than Sonic in size. Some notable features of this design include the almost chainsaw-like way his spines can rotate, its eyes which now resembled Sonic's in shape but are black and have a single red pupil, the wheels in his heels and his armor. This version made a cameo in Sonic Adventure with a slightly different design.

Trivia

 * The character gained much more online notoriety after the Sonic and Knuckles design was used as the major antagonist of the sprite-based web show Super Mario Bros. Z. This show is actually how many Sonic fans learned of the character in its original form.