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