This is the only spell that will instantly create at least one minion without any corpses, although it is most beneficial with many exploitable corpses around. Two other skills capable of creating a minion without a corpse are available exclusively from Kuunavang in certain areas where she is present.
The Death Magic increase occurs last, after creating the minions.
It is useful to re-cast this spell as soon as it is recharged, adding at least one more "free" minion to your army.
If this spell is re-cast before its effect expires, it will affect itself. The attribute bonus will not stack, and will still be only +1 Death Magic over your base attribute rank, however you will benefit from higher level minions and longer duration.