Here is the full list of all 21 Solo: Islands of the Heart trophies - there are 2 bronze, 10 silver, 8 gold and 1 platinum.
Earn all trophies
Complete the game by boat.
Complete the game talking on the bench.
Complete the third archipelago.
Feed all the animals in the game.
Help the last Puchuchu on the third archipelago to be together.
Water the flowers on the third archipelago.
Help the first Puchuchu on the third archipelago to be together.
Gather all the songs.
Complete the second archipelago.
Help the last Puchuchu on the second archipelago to be together.
Interact with all the ghost partners.
Water the flowers on the second archipelago.
Photograph a fish for the sapling and give it to him.
Help the first Puchuchu on the second archipelago to be together.
Complete the first archipelago.
Photograph a red seagull for the sapling and give it to him.
Water the flowers on the first archipelago.
Help the Puchuchu on the first archipelago.
Lay on the beach.
Pet a hiding mole.