The Sacrament of Kedasnutael

1 Caster of 9th Level, who will become the Commander of the horde and no less and no more then 4 Assistants (each of which will be able to control 25% of the Horde [250 Undead])
The caster must be a Lich that can cast 9th level spells, the ritual take 7 days during which if any of the assistants or the caster are killed disintegrates all the corpses used during the ritual cursing each living creature within 2 Kilometers to die slowly with no hope of survival (1d4 Necrotic damage per day, once a creature is dropped to 0 they fall comatose and start dying) and instantly slaying the rest of the assistants and/or the caster, each subsequent casting from the caster requires 4 new assistants.

"Created long ago by the Balor Kedasnutael under the orders of a Lich who's name has been lost to history, in order to create an army of Undead with which Kedasnutael's master could invade neighboring kingdoms however out of spite Kedasnutael added a flaw to the spell that proved to be the undoing of his master, during the ritual Kedasnutael struck down one of the assistants that were the soon to be generals shattering the Lich's Phylactery and dragging the unfortunate souls into the Abyss, only a caster who has sealed their soul within a item can cast this spell and should tread lightly while doing so since Kedasnutael actively seeks out Casters who would attempt to cast this spell since if a Devil of considerable power should be there instead the souls of the dead wouldn't be going to the Abyss and Kedasnutael will be one step further away from becoming a Demon Lord."