the horned people are like the religious dictators (although they are generally good ppl) of gridania. they commune with the elementals and build the hedge which is a man-made magical construct to protect the forest.

The ascians will be part of 2.0

And Leviathan is the primal of the sahagin i believe, which are at war with limsa lominsa. They are -supposed- to be in some of the current zones (like the dungeon by bloodshore) but were never implemented (lore/npcs/leves say they are there)

Also the Sahagin inhabit various islands around la noscea

The ppl in limsa however believe that leviathan is a mythical seamonster and not necessarily real. Ppl also don't like you talking about it.