Newbie Question about Desert Tombs

[tinkthank]

Ah right, my mistake was no death on my pretender.

Two follow-up questions:
1. What does the spell "blessing of the grave" (etc) do? It says "activates the power of an undead troop", but what does that mean? Does it give them a bless effect as if they were holy, or what?
2. It seems you need a whole lot of death gems to summon those more powerful unholy priests. Are they worth it?
Other question: What scales do you take? You need death and heat, and that death hurts -- so do you take order, or luck, or what?
thanks a lot