Periodically, you will encounter friendly creatures in battle who will ask for various items (Ore, Moonstone, etc). These creatures are the Land Spirits. You don't have to help them out, but if you don't help them, you will never be able to reach Ozma. I strongly recommend you help them out by giving them the items they request.
Below is a chart of the Land Spirits, including where you can find them and what items they will request. Once you meet the final Land Spirit (a Yan), it will tell you that you can reach ``the big round guy'' now. The ``big round guy'' in question is Ozma, who is impossible to reach with short-range physical attacks up to this point.
|Mu||1x Ore Stone||Found around the village of Dali|
|Ghost||1x Ore Stone||In front of Treno, or around South Gate, and in-between|
|Ladybug||2x Ore Stone||Ladybug can be found around Black Mage village, in the forest surrounding it|
|Yeti||2x Ore Stone||Yeti can be found in the forest around Madain Sari|
|Nymph||3x Ore Stone||Nymph can be found in the only forest by the Iifa Tree|
|Jabberwock||1x Emerald||Jabberwock can be found in the forest east of Oeilvert|
|Feather Circle||1x Moonstone||Feather Circle can be found on the Lost Continent (the snowy continent). Run along the Chocobo tracks (near the southern beach of the continent) to encounter Feather Circle.|
|Garuda||1x Lapis Lazuli||Garuda can be found on the outside of Gizamaluke Grotto, after climbing the rope near the save point located within it.|
|Yan||1x Diamond||Yan can be found on Vile Island (the big island near the center of the world map). Be sure you have found all other 8 Land Spirits, or else Yan will run away.|