Doom (5e Spell)
From D&D Wiki
You target a creature within range that has a challenge rating of 50 or lower and is Huge or smaller. It must succeed on a Constitution saving throw or be doomed by you. If a creature is already under the effect of a doom spell at a higher level when you cast this, both spells end and the creature takes 20d12 necrotic damage. Otherwise, after 1 minute, the creature takes 15d12 necrotic damage.