Vigor Sense

As part of the casting of this spell, you must expend 2 hit dice or the spell fails automatically. If you do so, you can sense the vitality flowing within creatures you can see. For the duration of the spell, you can sense whether and how two or more creatures are related biologically. In addition, you know whether the creature's current hit points are equal to or below half their maximum hit points and, when you deal damage to such creature, you roll two additional dice to deal bonus damage. The dice rolled to determine this bonus damage are the same as the two you expended to cast the spell. (Your hit dice type)

At Higher Levels. When you cast this spell with a 4th or 5th level spell slot, you can maintain concentration on this spell for up to an hour. When you cast this spell using a 6th level or higher spell slot, you can maintain concentration on this spell for 8 hours.