[Executor]

Oh, I agree they are perfectly good with only 1 at a time, that high defense and glamor really increase the survivability rate, not to mention their life drain attack and they're only 2 gems.
I just find them hard to summon cause the Kings, which are meant to summons them, are always tied up fighting somewhere, at least in my case, never was one to idly sit by...

As for Valkyries, probably the best spell Fomoria has in their arsenal. A few Kings can summon quite a bunch of them.