Here is the full list of all 51 Coral Island achievements.
Earn 50k coins
Gain access to Giants’ Village
Slay 10 enemy types
Gain access to Merfolk Kingdom
Give a gift to 25 NPCs
Reach heart 5 with an NPC
Earn 20k coins
Ship one crop 1000 times
Harvest 100 crops
Earn 100k coins
Earn 250k coins
Earn 500k coins
Earn 1000k coins
Earn 10000k coins
Complete artifact collection
Complete gem collection
Complete dinosaur collection
Complete bug collection
Complete fish collection
Complete sea critter collection
Complete museum collection
Clear all the mine gates
Heal all the sick coral
Restore the temple
Reach heart 8 with an NPC
Reach heart 10 with an NPC
Reach heart 5 with 25 NPCs
Reach heart 8 with 25 NPCs
Reach heart 8 with All NPCs
Give a gift to all NPCs
Start dating an NPC
Get married
Have 2 children
Cook 15 recipes
Cook all recipes
Craft 15 things
Craft all things
Purchase 10 clothing items
Purchase 50 clothing items
Purchase all clothing items
Slay 20 enemy types
Slay all enemy types
Ship 30 different crops
Ship all crops
Ship 2 animal products
Ship 5 animal products
Ship all animal products
Ship a golden animal product
Ship everything in the game
Ship one animal product 1000 times
Reach level 10 mastery in everything