Here is the full list of all 50 The Spiderwick Chronicles achievements worth 1,000 gamerscore.
Finished an ISL match in which each player scored 50+ points.
Scored 100 points in a "Sprites and Goblins" ISL Arena match without taking damage.
Completed a multiplayer match in every ISL Arena.
Finished Chapter Eight.
Recorded all Bellflower Sprites.
Recorded all Pond Skater Sprites.
Recorded all Flower-Head Sprites.
Recorded all Sprout Sprites.
Recorded all Stray Sod.
Completed the Cockatrice page of the Field Guide.
Obtained Hobgoblin spit for Simon.
Fully decorated Thimbletack's house.
Completed Garden Sprites quest.
Completed River Troll page in the Field Guide.
Recorded all Leatherwing Sprites.
Collected all Flower-Winged Sprites.
Collected 40 Faerie Fruit.
Completed the Fire Salamander page in the Field Guide.
Obtained Hobgoblin spit for Mallory.
Collected 50 Roaches.
Finished Chapter Seven.
Finished Chapter Six.
Collected 100 Ball Bearings.
Collected 500 Goblin Teeth.
Recorded all Beetle Mimic Sprites.
Finished Chapter Five.
Recorded all Royal Orchid Sprites.
Collected 100 Gobstones.
Collected 50 Gobstones.
Talked to both Knockers.
Recorded all Will O' The Wisps.
Completed the Griffin page in the Field Guide.
Completed the Redcap page in the Field Guide.
Finished Chapter Four.
Collected 250 Goblin Teeth.
Sent a Goblin into a Fire Salamander with a Distract Sprite.
Collected 25 Gobstones.
Trapped a Goblin inside a Toadstool Ring.
Collected 10 Fire Salamanders.
Finished Chapter Three.
Collected 100 Goblin Teeth.
Collected 50 Ball Bearings.
Collected 20 Faerie Fruit.
Sent a Goblin over a cliff with a Distract Sprite.
Collected 25 Ball Bearings.
Collected 10 Faerie Fruit.
Finished Chapter Two.
Collected 25 Roaches.
Collected 10 Roaches.
Finished Chapter One.