Cull the Weak

You extend a finger at a creature and from it, black lightning streaks out, chaining to nearby creatures.

One creature you can see within range makes a constitution saving throw. Upon failure, the creature takes 2d8 necrotic damage. After this, the closest creature to it must make the same saving throw with the same fail conditions. This repeats until a creature succeeds their saving throw. On a successful saving throw, a creature takes half damage and the effect no longer spreads.

For each level above 3rd that you cast this spell at, add 1d8 damage to the spell and increase the spell save DC for this spell by 1.