Instructions
Play through the stage "Misty Lake 2" and meet King Arthur at the end. Unlike the King Arthur of legend, this Arthur is a coward and will spend most his time fleeing. As soon as Sonic sees him, Arthur will run.
Chase King Arthur until he stops. Wait until a blue Wii controller appears on the screen. Immediately begin shaking the Wii controller until the icon disappears.
Shake the controller again when the icon reappears. A large "A" will eventually appear on the screen. Press the "A" button on the remote. Sonic will strike King Arthur with his sword, but it isn't yet enough to defeat him. Arthur will run again.
Evade other enemies when they arrive and focus on chasing King Arthur. Sonic's speed will easily outpace them. Eventually, King Arthur will stop again. Shake the Wii remote when prompted and then press the "A" button. Sonic will strike, and King Arthur will flee once more.
Give chase a final time, evading enemies when they appear. When King Arthur stops again, shake the remote and push the "A" button once more. This time, the strike will finish Arthur off.