Rare Loot you have the small chance of obtaining if you turned in 10 or more Hearts of the Sea to Qjell during the last Deepling stage 1 world change, when it changes to Stage 2 you will gain access to a Teleport to a reward room with a blue Treasure chest and Hoards of Gold. From these you have a small chance of looting a True Heart of the Sea
Sorry, i dont know and couldnt find the odds of looting it