This list of mythical creatures that begin with this letter and I am constantly gathering information from each continent, and is continually being updated.
Jasy Jaterei (Guaraní)
Jasy Jatere, which means literally "a little piece of the moon", is unique among his brothers in that he does not have a monstrous appearance. He is usually described as being a small man or perhaps a child, with light blonde hair and sometimes blue eyes. He is fair in appearance, sometimes described as even beautiful or enchanting, and carries with him a magical wand or staff, sometimes described as a golden cane, although what clothing he wears, if any at all, does not seem to be an important part of the legend.
Like most of his brothers he dwells in the wild, he is considered to be the protector of the yerba mate plant. Sometimes he is also viewed as a protector of hidden treasures. It is said that Jasy Jatere's power stems from the magical staff that he carries, and if one is able to take it from him, he breaks down and cries like a little child. In this state, one may ask him for the treasures that he is protecting in return for the staff, not unlike a captured leprechaun who must reward his captor with a pot of gold.