Here is the full list of all 48 Where the Wild Things Are achievements worth 1,000 gamerscore.
Complete 'Arrival'
Complete 'Road to Nowhere'
Complete 'The Cave'
Complete 'Canyon River'
Complete 'Seasick'
Collect 25 Geodes
Collect 25 Seeds
Collect 25 Skulls
Collect 25 Houses
Find 5 Stars
Find 20 Stars
Find 40 Stars
Defeat 250 Fireflies
Defeat 100 Shadow Creatures
Earn 4 Hearts
Earn 7 Hearts
Be eaten by three different Wild Things
Allow three different Wild Things to fade into oblivion
Power-swing from three bars
Defeat five enemies with one firefly bomb
Complete a Sailing mission without crashing
Start a Dirt Clod Fight with multiple Wild Things
Defeat 15 enemies in a row in melee without being hit
Complete a ride with Carol without crashing
Find 95 Stars
Collect all Turtles
Collect all Honeycombs
Collect all Owl Eggs
Collect all Seeds
Complete the game on Hard
Complete the game on Normal or higher
Complete the game on Easy or higher
Complete 'A Trip to the Moon'
Collect all Houses
Collect all Skulls
Earn 10 Hearts
Collect all Geodes
Complete 'Below the Roots'
Collect 25 Turtles
Complete 'Setting Sail'
Find 65 Stars
Complete 'Old Willow'
Cause three different Wild Things to sneeze
Complete 'Crumbling Island'
Collect 25 Owl Eggs
Complete 'Rebellion'
Collect 25 Honeycombs
Defeat 25 Lightning Bugs