Here is the full list of all 21 The Peanuts Movie: Snoopy's Grand Adventure achievements worth 1,000 gamerscore.
Defeated The Mask Boss without being hit
Found all the kids
Completed all Skies of Paris levels
Completed all Melody Chateau levels
Completed all Parisian Underground levels
Unlocked all Costumes
Unlocked the Detective Costume
Collected all Jelly Beans in a single level
Unlocked the Joe Cool Costume
Completed all Lunar Surface levels
Broke through a wall as the Masked Marvel
Unlocked the Masked Marvel Costume
Unlocked the Flying Ace Costume
Completed all Temple of Bunnies levels
Jumped on three enemies without touching the ground
Unlocked the Astronaut Costume
As normal Snoopy hovered for more than 5 seconds
Completed all Peppermint Jungle levels
Unlocked the Beagle Scout Costume
Level finished
Collect all kids objects