Aranaidas' Call of the Grave

You cause the ground beneath your enemies to boil and churn like a hungry grave, seeking to consume them.

Each creature in the area must make a Wisdom saving throw (DC based on the caster’s spellcasting ability) at the start of its turn. On a failed save, the creature is Stunned until the start of its next turn as its soul is pulled toward the grave.

If a creature starts its turn in the same space where it previously failed, the ground fully swallows it, and a nameless gravestone emerges in its place.

• The creature is transported to a shadowy plane of death, where it must succeed on a Charisma saving throw (DC based on the caster’s spellcasting ability) each turn to attempt to return.
• While trapped, the creature cannot be targeted by spells or abilities from the material plane.
• An ally can touch the gravestone and use their action to attempt a rescue, giving the trapped creature a chance to repeat its Charisma saving throw with advantage.
• If the creature fails three Charisma saving throws in a row, it becomes permanently trapped within the grave, its name appearing on the tombstone. Only using a spell such as Wish or True Resurrection can release it.

At Higher Levels:

When cast with a 9th-level spell slot:

• Trapped creatures lose 10 maximum hit points for every turn they remain inside the grave. If their maximum hit points reaches 0, they suffer Permanent Death and can never be brought back to life by any means short of a Wish.
• They cannot receive external aid unless an ally sacrifices themselves to take their place.