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