Here is the full list of all 50 The Spiderwick Chronicles achievements worth 1,000 gamerscore.
Find the Field Guide.
Obtain the Monocle.
Burn the Field Guide.
Find Aunt Lucinda.
Tame the Griffin.
Return to the Mansion.
Defeat Mulgarath!
Complete the Field Guide.
Collect 10 Cockroaches.
Collect 25 Cockroaches.
Collect 50 Cockroaches.
Collect 25 Gobstones.
Collect 50 Gobstones.
Collect 100 Gobstones.
Collect 25 Ball Bearings.
Collect 50 Ball Bearings.
Collect 100 Ball Bearings.
Collect 10 Faerie Fruit.
Collect 20 Faerie Fruit.
Collect 40 Faerie Fruit.
Collect 100 Goblin Teeth.
Collect 250 Goblin Teeth.
Collect 500 Goblin Teeth.
Collect 10 Fire Salamanders.
Record all Leatherwing Sprites.
Record all Royal Orchid Sprites.
Collect all Flower-Winged Sprites.
Record all Flower-Head Sprites.
Record all Will O' The Wisps.
Record all Bellflower Sprites.
Record all Stray Sod.
Record all Sprout Sprites.
Record all Beetle Mimic Sprites.
Record all Pond Skater Sprites.
Complete the Fire Salamander page in the Field Guide.
Complete the Cockatrice page of the Field Guide.
Complete the Griffin page in the Field Guide.
Complete the Redcap page in the Field Guide.
Complete River Troll page in the Field Guide.
Talk to both Knockers.
Complete Garden Sprites quest.
Trap a Goblin inside a Toadstool Ring.
Send a Goblin over a cliff with a Distract Sprite.
Send a Goblin into a Fire Salamander with a Distract Sprite.
Complete a multiplayer match in every ISL Arena.
Finish an ISL match in which each player scores 50+ points.
Score 100 points in a "Sprites and Goblins" ISL Arena match without taking damage.
Fully decorate Thimbletack's house.
Obtain Hobgoblin spit for Simon.
Obtain Hobgoblin spit for Mallory.