Resurgence
Circles: Death, Biomancy
Description: Target destroyed Zombie or Skeleton unit is brought back to life (or undeath!) at 70% health.
This one probably doesn't need a great deal of debate. It's simply a negative energy “raise dead” spell.
At first it may not seem super useful, but keep in mind that The Unhallowed aren't mindless undead. They gain experience and levels. Bringing back an elite unit of Skeletal Archers is going to be a lot better than just making new one. Because of this I think it's a good fit.
Thoughts?