Here is the full list of all 12 Pac-Man Championship Edition achievements worth 200 gamerscore.
Complete Challenge Mode 2!
Complete Challenge Mode 1!
Complete Extra Mode 3!
Score 400,000 points!
Eat the Crown!
Complete Extra Mode 2!
Complete Extra Mode 1!
Score 200,000 points!
Eat 8 ghosts in succession!
Eat the Key!
Complete Championship Mode!
Emit sparks for 1 second!