Here is the full list of all 41 Castle on the Coast achievements.
Unlock all costumes
Unlock Aleandra's costume
Activate the hidden player 2 camera mode
Reach the highest point of the castle. Wow!
Drive a submarine into the library?
Reach the top of the distant, ocean tower
Reach the peak of one of the large, distant mountains on the mainland
Escape the confines of the playable castle area
Collect every star
Collect every moon star
Unlock the secret costume
Play the world's largest musical instrument
Discover the secret ocean
Collect every orb star
Unlock Vendrick's costume
Unlock the mecha costume
Take down 15 suites of armor
Customize your appearance while wearing the kid costume
Collect every spiky star
Beat the game!
Obtain the ocean's keystone
Drive a car into the library
Defeat 20 of your bretheren in wood
DETONATE your save file.
Defeate Vendrick and obtain the rainy cathedral keystone
Bounce off a character 30 times
Bounce off a character 10 times
Spin a character 30 times
Spin a character 10 times
Cheerfully wave 30 times
Turn on co-op mode
Accumulate 1,000 unspent petals
Obtain the stunt park's keystone
Defeate Aleandra and obtain the forest keystone
Survive an alternate dimension
Taste defeat for the first time.
Make friends with a shark, awwwww...
Find a hidden ball
Unlock your first costume
Unlock the jetpack
Arrive at the Castle on the Coast