Assassin's Mark (PoE)

Curses a single enemy, making it more likely to land critical hits. 

  The number you needed to roll a critical hit is reduced by 1. Additionally, when you land a critical hit, you deal an additional 1d6 damage of the same type as your weapon against the marked creature.

If the target drops to 0 hit points before this spell ends, 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.