As the title reads, I would love to see some unseen enemies and environmental challenges implemented into FFXIV.
A few examples I can pull from FFXI are:
Unseen Enemies - the only ones that come to mind are the antlions in Attohwa Chasm and to some extent (because you can actually see them) the UFOs in Sea
Environmental Challenges - again in Attohwa Chasm, the large hill/mountain you had to climb without falling off; the pitfalls in Uleguerand Range; and the trap doors/combination puzzles in Castle Oztroja
I really do believe we need challenges of this sort to make Eorzea feel more alive, and dangerous. Maybe they could add an entire dungeon that is a labyrinth with puzzles to complete, rewarding players with different treasures based on their performance. I also love the idea of mobs we can't physically see, but must be very aware to avoid.
Another example I can pull from FFXI (also from Attohwa Chasm lol, what a zone!), are the plants that poisoned you as you walked by. I think it would be great to see more of the natural environment be a threat to the player. Anything that keeps me on my toes and is more challenging, makes for a better game imo.
Falling rocks, collapsing bridges, dangerous hidden fauna, pitfalls, trapdoors, secret combination treasure rooms, ANY of these things SE, please add some depth and flavor to these very bland and forgettable (yet nicely rendered) environments.