This list of mythical creatures that begin with this letter and I am constantly gathering information from each continent, and is continually being updated.
Jentil (Basque)
The jentil were believed to have lived alongside the Basque people. They were hairy and so tall that they could walk in the sea and throw rocks from one mountain to another. This stone throwing has led to several tales and explanations for ancient stone buildings and large isolated rocks. Even the Basque ball game, pilota, is ascribed to these stone-throwers.
The tradition lives on in the Basque power games of stone lifting and throwing. Some attributed to the jentil the defeat of Roland in the Battle of Roncevaux, where the Basques defeated the Frankish army by throwing rocks on them. The giants were believed to have created the neolithic monuments, such as dolmens, found around the Basque Country.