Stalker’s Eye

Enchantment cantrip

Casting Time: 1 action
Range: Touch
Components: V, S, M (small magnifying lens)
Duration: Concentration, up to 1 minute
Class: Bard, Druid, Tamer

A willing creature you touch gains a preternatural ability to perceive the weaknesses in a creature’s defences. The first time the creature makes an attack while under the effect of this spell, it makes the attack with advantage. After it makes an attack, the spell ends.

At Higher Levels. This spell augments the creature’s ability to strike at vital points when you reach certain levels. When you reach 5th level, the augmented attack scores a critical hit on a roll of 19 or 20. At 11th level, this range is increased to 18 to 20, and at 17th level, this range becomes 17 to 20.

Source: Heliana's Guide to Monster Hunting