Here is the full list of all 12 Castle of Pixel Skulls DX achievements worth 1,000 gamerscore.
Finish Level 20
Finish Level 15
Die 20 times
Finish Level 10
Die 10 times
Finish Level 5
Die 5 times
Jump 40 times
Finish Level 1 without dying
Finish Level 1
Jump 25 times
Jump 10 times