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