QM:
I think that both Leprosy and Black Death would be viable at 8-10D gems per casting. Black Death is level4? Huh, I thought it's level 7[which it definetely should be, well, at least 6]. And QM knows why the cost of Black Death can be not so big
There are wars you don't win. Or those where you don't care for spoils. Black Death is a nasty spell, but not really great against bigger enemies, as their income is really distributed.
And could you maybe add a small item pack? Water and fire could really use more items. Especially water. Use of W gems is really boring