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