Here is the full list of all 39 Rainbow Billy: The Curse of the Leviathan achievements.
Break the Curse of the Leviathan and save the World.
Climb to the highest point in each area of the World.
Befriend all creatures.
Raise 40 creatures' friendships to Level 3!
Peek through the window...
Accept your other self and befriend Shadow Billy.
Get reprimanded for punching barrel-kind.
Collect ALL Thought Upgrades!
Collect 75 Thoughts.
Raise 30 creatures' friendships to Level 2!
Hear each and every one of the The Confessor's secrets.
Glide using the Billy-Copter for more than 5 straight seconds!
Raise 20 creatures' friendships to Level 3!
Collect 50 Thoughts.
Face your fears and befriend Calypso.
Talk to all Kickstarter Backers characters!
Flawlessly complete a difficult "Dodge" attack minigame!
Own 500 coins or more.
Collect 25 Thoughts.
Fast travel between two distant areas of the World.
Discover the broken warp pipe.
Discover Disco Broccoli!
Dig up 15 buried treasures.
Fight toxic masculinity and befriend Dragalant.
Flawlessly complete 50 attack minigames!
Catch 10 non-gummi items while fishing.
Recolor five colors in one blow!
Flawlessly complete a difficult "Circle" attack minigame!
Flawlessly complete a difficult "Paddle" attack minigame!
Collect 10 Thoughts.
Flawlessly complete a difficult "Slots" attack minigame!
Raise 5 creatures' friendships to Level 2!
Catch three different objects in one fishing session!
Flawlessly complete a difficult "Line" attack minigame!
Destroy 25 Objects!
Convert a Thought into a Figment of Imagination!Service.
Listen to Friend-Ship whistle for more than 5 straight seconds.
Raise ALL creatures' friendships to Level 3!
Catch at least one of each kind of fish!