The Goal Of All Life Is Death

You utter a phrase of dark power and as you do so, an arcane clock of dark energy that measures 10ft in diameter hovering 5ft above the ground appears behind you that ticks down from 3,2,1. And as it chimes, all creatures of your choice that you can see within 90 feet of you must make a Constitution saving throw or take 12d12 necrotic damage on a failed save and half as much damage on a successful one. This spell ignores necrotic resistances and immunity's and doesn't affect constructs or undead.