As I recall the pearl is in one of the passages in home waters under the turtle (on the bottom right, below the passage to open waters and the one from the start of the game); you need bind form to drag it into Naija's home and place it in the mouth of the stone face holder , and energy form to charge it up (press control or right-click) so that the passage opens; there's a song plant and if all you have is energy form, the tooth from the energy boss. Some stuff goes into passages below the house that require beast form to access, and the currents in the cave behind the pearl also require beast form; some of the Mithalas treasures go there. Also you will need nature form to access the bluish metal looking transport ball which takes you to another area when you get the seed bag from the Kelp Forest. A number of the maps are incomplete and get bigger as you find more forms and treasures.
