Some kinds of magic items don't necessarily have great power in and of themselves, but blended with something else in just the right way and you have a terrifying power at your fingertips.
Wondrous item, uncommon
A hag’s eye looks like a perfectly preserved human eyeball, watery and slightly yellow with an enlarged iris. Hag’s eyes have different effects depending on their color. When added to a potion, a hag’s eye dissolves completely, leaving no trace. Identifying a potion tainted with a hag’s eye requires a DC 14 Intelligence (Arcana) check.
Brown: The drinker becomes extremely thirsty and must succeed at a DC 14 Constitution save or gain a level of exhaustion. The exhaustion persists until he drinks 10 gallons of water, at which time the creature removes the level of exhaustion.
Hazel: The drinker must succeed at a DC 14 Wisdom saving throw or fall asleep for one hour.
Blue: The drinker must roll a Wisdom save. On a failure, they gain the ability to Scry on the subject as per the spell scrying, unless the drinker makes a DC 14 Wisdom saving throw. Modifiers apply as per the spell if any conditions apply.
Green: The potion becomes especially appetizing. Anyone offered the potion must succeed at a DC 14 Charisma save or drink it immediately. Creatures immune to the charmed condition are immune to this ability.