The Eye of Argos

 You gather your mana and filter it through your eyes. As it spreads through your vision you perceive the weak points of the creature you look upon. The effected creature must succeed on a DC15 Wisdom saving throw or be inflicted with the Revealed Blood condition for 3 turns. 

When attacking creatures effected by this condition, the attackers dice role needed for a critical damage is decreased by 1. (20 to 19 by default)

When cast with higher levels it can target an additional creature per spell slot level. Additional, when cast at 5th level the condition last for 4 turns instead of 3, and when cast at 8th level it will last for 6 turns.