What's so great about Nanaly? I managed to get her (my only black card) through the rare summon (by not obeying the guide and pressing it when I only had 5 crystals... but I already wasted so many silver units before I found this site that I've only managed to class evolve one, everything else is still unevolved and not likely to be any time soon). I find myself wishing I had found a rare mage or something instead, she doesn't do so well against things in armour and the "retake the castle" story mission is absolutely crushing me when the huge horde comes running out.

That said, these event missions are also kind of crushing me, and I've got my main force all up to around level 30 at this point. Rough. I got 2 stars on the first, 1 on the second, and the third makes me wince a lot.