Here is the full list of all 13 Fluffy Milo achievements worth 1,000 gamerscore.
Complete Level 1.
Complete Level 5.
Complete Level 10.
Complete Level 15.
Complete Level 20.
Complete Level 25.
Complete Level 30.
Complete Level 35.
Complete Level 40.
Complete Level 45.
Complete Level 50.
Complete Level 55.
Complete Level 60.