Epic Spell: Momento Mori

As a bonus action, you can will a creature dead without a word or gesture. With a thought, you snuff out the life force of a living creature within 300 feet of you that has fewer than 20 Hit Dice, killing it instantly. The target must make a Constitution saving throw or be instantly slain. On a successful save, the target instead takes 20d10 necrotic damage.

Creatures with 20 or more Hit Dice automatically save against this spell.

For all intents, purposes, and interactions this spell is treated as a 10th level spell.