World Entrance Level 2

Metal Sonic Kai (メたl ソにc カい) is a transformation of Metal Sonic and is the final boss of Knuckles' Chaotix. It is sometimes called Mega Metal Sonic, Emperor Metallix, Project: Chaotix, and Super Metal Sonic (although the Super prefix is generally misleading).

Metal Sonic Kai is a huge, red version of Metal Sonic, with a slighlty elongated, cat-like face.

History
After losing to the player, (it can be any member of the Chaotix), Metal appears to Dr. Robotnik. After turning another Chaos Ring into a Dark Ring, the Doctor motions Metal to enter the ring. With the power if the Dark Ring, Metal Sonic transforms into a huge, red, cat-like mechanical being and the Chaotix member (whichever the player chooses) and his partner fall into a square room with ten Rings in hand. During the first section, hit the body eight times to destroy the left and and Metal will go into the background and attempt to hit the player with his right hand. After another eight hits, his right hand will be destroyed and the robot will go to the left of the arena and will fire a huge laser, which can be dodged by ducking. After eight hits, the robot will be destroyed and if the player has all seven Chaos Rings, the good ending will play with the Rings disappearing and Sonic and Tails appearing in the Tornado behind the Chaotix. If the player fails to collect the Chaos Rings, Metal Sonic Kai will appear overlooking a burning area (possibly Newtrogic High Zone) and the player has to collect the rings again.

This fight can be very easy if playing as Charmy and Heavy. As Charmy is invincible while flying and Heavy is invincible in general.

Archie Comics
Metal Sonic Kai appears, again as a transformation of Metal Sonic, in the Knuckles' Chaotix special from Archie Comics. He is defeated by a similarly transformed Knuckles who used a Power Gem to defeat him since the Chaos Rings were completely absent in the comic.

Sonic the Comic
Metal Sonic Kai was thoroughly re-imagined in the series Sonic the Comic, and replaced by Emperor Metallix. Both were large, red versions of Metal Sonic (called Metallix in this continuity), but Emperor Metallix was a separate unit rather than a transformation. He was the leader of the Brotherhood of Metallix.

Emperor Metallix first appeared in the story "Total Chaotix" from Sonic the Comic #53 to #58, a loose adaptation of Knuckles' Chaotix.

Trivia

 * In Japanese, Kai can translate to either king, or meeting. In this case, Metal Sonic Kai can be called "Metal Sonic King" or "King Metal Sonic" to make more sense. Kai also roughly, or losely, translates into big.
 * Metal Sonic Kai is Metal Sonic's first super transformation.