This was the final boss of Knuckles' story in Sonic & Knuckles. While this is a relatively easy final boss, Metal Sonic's ability to absorb the energy of the Master Emerald to take on a super form was unexpected (although fitting to the story, which was that Dr. Robotnik tricks Knuckles into believing that Sonic is the one who is trying to steal the Master Emerald). Plus, this was the only boss in Sonic & Knuckles that was unique to Knuckles' story.