The Staff of the Necromancer was created a long time ago in secret by a council of thirteen powerful necromancers as a dark counterpart to the Staff of the Magi, infused with all aspects and spells of the school of necromancy known at that time. In fact, basically noone other than these necromancers knew of that staff's existence until recently, when a certain lich found it sealed away in an ancient library guarded by several undead - that probably was for the best. Once the seal was broken, the staff's baleful magic started to seep into the world again, calling forth undead, causing nightmares and feeding on souls, preventing them from reaching their afterlife.

The Staff of the Necromancer is made of withered ebony with long-forgotten runes of evil carved in it and stuck on its top is a dark-colored skull with ruby eyes and five pentagramms drawn on it resembling its charges.

This staff can be wielded as a magic quarterstaff that grants a +2 bonus to attack and damage rolls made with it. While holding it, you have immunity to necrotic damage and gain a +2 bonus to spell attack rolls and to your spell save DC.

The staff has 25 charges for the following properties. It only regains charges by feeding on souls with its soul siphon. If you expend the last charge, roll a d20. On a 1, you die and the staff absorbs your own soul.

Marshal Undead. You and any undead of your choice within 60 feet of you have advantage on saving throws against abilities that turn undead. In addition, as a bonus action, you can expend up to 5 charges to force a number of undead of your choice equal to the number of charges expended to use their reactions to move up to their speed and to make one weapon attack against a target of your choice. If an undead wants to resist your command, it can do so by succeeding on a Wisdom saving throw against your spell save DC.

Soul Siphon. When a creature drops to 0 hit points within 60 feet of you, you can use your reaction to cause the staff to absorb its soul, killing it in the process. The staff then gains a number of charges equal to the creature's CR, provided it has a CR of at least 1. Constructs and undead are immune to this ability, and if absorbing a soul would bring the staff above its maximum capacity of 25 charges, the soul cannot be fully absorbed; it instead is torn asunder in a burst of necrotic energy. The staff is charged up to its maximum capcaity and each creature within 60 feet if the staff must make a DC 17 Constitution saving throw, taking necrotic damage equal to five times the amount of excess charges the soul would have granted or half as much on a success.

In addition, any humanoid soul successfully absorbed by the staff can be used as if you had cast soul cage on it.

Vampiric Strikes. When you hit a creature with a melee attack using the staff, you can expend 1 charge to deal an additional 21 (6d6) necrotic damage to the target. You regain hit points equal to the necrotic damage dealt.

Spells. While holding the staff, you can use an action to expend some of its charges to cast one of the following spells from it, using your spell save DC and spellcasting ability: Abi-Dalzim's horrid wilting (8 charges), animate dead (3 charges), bestow curse (3 charges), blindness/deafness (2 charges),  circle of death (6 charges), create undead (9th-level version, 9 charges), finger of death (7 charges), negative energy flood (5 charges), power word kill (9 charges),  shadow of moil (4 charges), tether essence (7 charges), time ravage (9 charges), or wither and bloom (9-th level version, 9 charges).

You can also use an action to cast one of the following spells from the staff without using any charges: chill touch, find familiar (summons a crawling claw), protection from evil and good., ray of enfeeblement, sapping sting, or speak with dead.

Random Properties. The staff has 1 minor beneficial properties, 1 major beneficial property, 1 minor detrimental property and 1 major detrimental property.

Curse. The staff is cursed and attuning to it extends the curse to you. While under the effect of this curse, you are unable to voluntarily end your attunement to the staff and you are unwilling to part with it, keeping it within reach all the time. Wails and whispers of tormented souls you siphoned with the staff are always in your mind giving you disadvantage on Wisdom (Perception) checks, and when the staff is not fully charged, you suffer nightmares and feel compelled to satisfy the staff's hunger. When you attempt to do a long rest while the staff is not fully charged, you must succeed on a DC 17 Constitution saving throw or gain no benefit from the rest. If you fail this saving throw three times, you gain a long-term madness.

Destroying the Staff. The ritual that was performed to create the Staff of the Necromancer likely is lost in history, but there is a slim chance of the tomes detailing it still being conserved in some forgotten library or ancient tomb of horrors - or at least parts of them. To destroy the staff, the ritual must be performed in reverse order by a creature of good alignment under the effect of a holy aura spell. Otherwise, the ancient hero whose skull surmounts it must be brought back to life, no easy task considering the fact that the soul was imprisoned for the ritual back then, and then that hero must attune to both the Staff of the Magi and the Staff of the Necromancer and use the Staff of the Magi's retributive strike. Once the staff has been destroyed, all souls siphoned by it are restored and released into their respective afterlife.

Notes: Bonus: Magic, Bonus: Spell Attacks, Advantage: Saving Throws, spellcaster, Damage, Control, Detection, Combat, Deception, Warding