Utterdark Blast

Prerequisite

eldritch blast cantrip

Description

As a bonus action, you cause your fingers to blacken and exude the putrid smell of dead flesh. The next time you cast eldritch blast, each of its attacks deal necrotic damage instead of force damage. Choose one living creature hit by these attacks to make a Constitution saving throw. On a failure, the target’s hit point maximum is reduced by an amount equal to the total necrotic damage taken by these attacks. This reduction lasts until the target finishes a long rest. The target dies if this effect reduces its hit point maximum to 0.
You lose the benefits of this eldritch invocation if you use a different eldritch invocation that changes the damage type of your eldritch blast before you cast the cantrip.