Areon's Mark of Death

Choose a creature that you can see within range, and make that creature "Marked for Death" until the spell ends. You deal an extra 1d6 necrotic damage to the marked creature whenever you hit it with an attack.

If the marked creature drops to 0 hit points before this spell ends, you may choose to spend and roll one of your unspent Hit Dice and regain a number of hit points equal to the roll, and you can use a bonus action on a subsequent turn of yours to mark a new creature.

At Higher Levels. When you cast this spell using a spell slot of 3rd or 4th level, you can maintain your concentration on the spell for up to 8 hours. When you use a spell slot of 5th level or higher, you can maintain your concentration on the spell for up to 24 hours.