Angrath's Dreadhorde Saga

You draw forth spirits from the ethereal plane at the cost of your own vitality. As part of the Initial Casting of this Saga, you sacrifice 22 Hit Points to shape your life essence into a physical form and create a Poltergeist under your control. This creatures, along with any other undead created by this saga, are friendly to you and your companions. Roll initiative for the summoned creatures as a group, which has their own turns. They obey any verbal commands that you issue to them (no action required by you). If you don't issue any commands to them, they defend themselves from hostile creatures, but otherwise take no actions.

Each round you maintain concentration on this spell, you Produce the following Persistent Effects:

Round 2-5. Sacrifice an additional 13 health to create an Indentured Spirit within range. Roll initiative for the spirit. On subsequent rounds, every Indentured Spirit shares the same initiative.

Round 6-9. Sacrifice an additional 13 health to create an Indentured Spirit within range. Roll initiative for the spirit. On subsequent rounds, every Indentured Spirit shares the same initiative. Additionally, if you control 5 or more undead at one time, you gain health equal to any necrotic damage those undead deal until the beginning of your next turn.

Round 10. Sacrifice an additional 13 health to create an Indentured Spirit within range.  At the end of your turn, all remaining undead under your control remain until your next long rest.

Losing concentration during this Saga's Duration causes all undead created by this spell to immediately drop to 0 hit points and disappear.