After you visit Bilibin and have talked to the Lord, you may be tempted to go through the cave that leads to Imil and Mercury Lighthouse. Do not do so. First, go to Kolima and Kolima Forest. Make it through the forest by moving logs and battling enemies. You will eventually meet Tret, the tree. After you talk to him, climb up the vines on Tret that are very easy to miss. Once in Tret, you will eventually battle him after exploring and puzzle solving. After defeating him, now go through the cave to Imil. You could beat Tret after you visit Imil, but you would have to go through the cave several times. After completing Mercury Lighthouse, fill the bottle that you got from Imil with the Water of Hermes. Then, go to Tret and give the water to him. He will then turn all of the persons who were trees back to people.