"Otherwise, the bones go to waste, don't they?"Raise Skeletons is a first-level Death Magic spell in Heroes of Might and Magic IV that costs two spell points and creates a stack of skeletons from any stack of living creatures with dead members.
Raise Skeleton works in a manner identical to Summon Spells, except that Raise spells are restricted in that there must be a unit with creatures to raise. What this means is that you must target either a live unit with dead members, or a completely dead unit stack, and that you are limited in the number of creatures you can produce by the number of fallen creatures from that unit.
If, for example, you can raise twenty skeletons per casting, and you cast it on a unit of 30 magi that once had 40 members, then you will raise ten skeletons (the ten fallen magi will be raised as skeletons). If the other 30 magi are killed, then you can cast the spell on the unit again, and get twenty more skeletons, and even once more to get the last ten.
The Necromancy Ward spell will prevent you from raising any creatures at all for the rest of the battle - unless you start removing it from stacks you want to raise.
The skeletons that this spell produces can be somewhat useful for screening your back line, or for retaliation fodder. Unfortunately, because it probably cannot be cast on the first turn, it will be of only limited use in most situations.
This spell is probably most useful not for Death, but rather for Order, whose level-two spellcaster unit, the mage, can cast it. As part of an early strike, say with ice bolts, magic fists, and maybe some titan ranged attacks for good measure, a large force of magi could raise a respectable number of skeletons, and perhaps early enough in the battle to make a difference.