There is no limit to how many spectral mobs you can have, just make sure that if your gonna have an undead army, get alot of blood.or you can use a heal staff.If you attack an enemy mob or player your spectral minions will attack it as well, this includes passive mobs.
The Necronomicon can only be crafted with five necronomicon pages bordering a square of rotten flesh. Necronomicon pages cannot be crafted, but can be found as random drops from bosses, in random chests, and by chance of being sold by villagers for a large sum of emeralds. They are sometimes inside of the starting chest if you select bonus chest at world generation.
These pages are most easily found in high-tier battle tower chests.
Using the Necronomicon to raise the dead Steps:
1. Create a Soul of a creature by Reaping it with a scythe or killing with a Soulsteal Augmented weapon.
2. Stand within 3 blocks of the soul/ souls (Multiple souls can be ReAnimated at a time).
3. Right Click and hold with the Necronomicon in hand till it completes its casting. (Cost 10 units of blood per soul) (Blood container must be in hotbar)
4. Tame the Newly spawned Spectral Pet with a Creepball. (Right click) *Newly tamed pets are sitting, right click with open hand to make them stand*
5. Feed the Spectral Pet blood if the player wished to extend the spawn life of the pet.