Dagil's Wall of Death

You create a wall of necrotic energy on a solid surface within range. You can make a wall up to 60 feet long, 20 feet high, and 1 foot thick, or can make a ringed wall up to 20 feet in diameter, 20 feet high, and 1 foot thick. The wall is opaque and lasts for the duration. When the wall appears, each creature within its area must make a Constitution saving throw. On a failed save, a creature takes 5d8 necrotic damage and the first time it drops to 0 hit points within the next minute, it instantly fails a death saving throw; on a successful save, it takes half as much damage without the other effect. You regain hit points equal to half the amount of necrotic damage dealt when the wall first appears.

One side of the wall, selected by you when you cast this spell, deals 5d8 necrotic damage to each creature that ends its turn within 10 feet of that side or inside the wall. A creature takes the same damage when it enters the wall for the first time on a turn or ends its turn there. The other side of the wall deals no damage.