This abacus has up to six crystal rods running parallel to each other across an ornate emerald frame, with ten discs of onyx and sapphire adorning each of the rods. Like a common abacus, each of the discs represents a number of a different factor. The discs on the bottom rod represent factors of 1. The discs on the second rod represents factors of 10. The discs on the third rod represent factors of 100, and so on until the sixth rod is reached at factors of 100,000.

Random Properties. This artifact has the following random properties, which you can determine by rolling on the tables in the “Artifacts” section of the Dungeon Master’s Guide: 

• 2 major detrimental properties
• 1 minor detrimental property
• 1 minor beneficial property

Keeping Count. This abacus is used to count the number of undead a creature has raised with Animate Dead. A creature does this by sliding the appropriate disc to the right of the abacus when adding undead, or to the left of the abacus when subtracting undead.

Whenever a creature casts Animate Dead on a pile of bones or a corpse, as part of the casting, they can add the undead creature or creatures on their abacus to their total undead count. Until an undead creature dies, or the spellcaster uses an action to subtract the undead, any undead creature thus counted will be under the spellcaster's control without the need to recast Animate Dead. As an action, a spellcaster can subtract any number of undead from their count. 

Intuitive Construction. The abacus grows or shrinks in response to the creature with whom it is attuned, maintaining enough discs and rods to count up to the total number of undead a creature could raise using all of their spell slots and abilities. While the intention of the keeping count ability is to maintain control over undead raised with the Animate Dead spell, this abacus can help a spellcaster maintain control over any undead it has the ability to raise and control organically, without the magic item. 

Necrotic Divide. A spellcaster can choose to use the abacus as a spell casting focus. Whenever a creature casts a spell with the abacus, they must first divide the total number of undead within their count by the level of the spell they wish to cast. The remaining number rounded down to the nearest whole is the remaining number of undead on the spellcaster’s count. For example, if a wizard has 93 undead on their count, and wishes to cast a 9th level Wish spell, they must divide their count by 9, leaving them with 10 undead left on their count. The undead sacrificed to cast the spell are obliterated into necromantic energy to fuel the casting of the spell so that no spell slots are used. 

Multiply Death. As an action, a creature attuned to this artifact can expend a hit die by rolling the die, and multiplying the total by the number of undead on their count. The undead on their count then multiply themselves to match the new count. However, nothing short of a Wish spell can restore the creature’s hit die; and their hit point maximum decreases accordingly. 

Destroying the Artifact. If a creature attuned to the artifact attempts to use it to cast a cantrip, the artifact is destroyed. Any creature within 100ft of the artifact (including the attuned creature) must make a DC 30 Constitution Saving Throw. On a failure they take 20d8 necrotic damage, and half as much damage on a failure. Any creature that dies from this is immediately transported as an undead into the presence of Orcus. 

Notes: requires attunement by a spellcaster with Animate Dead prepared