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