Throwing in my 2gil here as well.

I'm a Bard, and at the Behemoth fight last night I could barely do any damage to the boss because I could not see him. I died multiple times without ever even seeing anything (I just randomly took 5-6k damage). When I did get him to appear, it was only long enough to get off one shot before he was gone again. The monster being invisible means we cannot see where he is facing, nor do his AOE indicators show on the ground. The greatest challenge in that FATE was merely making the boss appear on my screen, and stay there for more than 2 seconds!