Discussion of the Necropolis faction.

While playing as a Necromancer, I noticed a peculiar ability: it deals damage to all living creatures and, on top of that, restores health to its own units. However, the "sacrifice" ability is unclear – does it transfer damage from one of your units to another, or can it be used to damage an enemy unit? Also, does the "Path of Tears" ability work similarly at higher levels? Could someone explain it in more detail?