The second palace boss is the one I had the most trouble with. Without spoiling anything, it consists of multiple separate parts that work together. Make sure you have some wind resistance, lots of healing items/abilities, and in the second phase you have to kill the two top parts at the same time or else they resurrect each-other. Other than him, I've had no trouble with the bosses. Maybe I'm getting lucky, but they all seem so easy since you can prepare for them. Boss 3 was by far the easiest, and 4 only gave me difficulty until I remembered one of my teammates had the ability to cure Despair