Despair Knives

Weapon Type: Dagger
Rarity: Legendary
Attunement: Required
Damage: 1d4 shadow damage

Magical Effect:

When a creature is hit by Despair, they must make a DC 15 Wisdom saving throw. On a failed save, the creature is cursed with despair. The creature is considered frightened until the end of their next turn.
The curse of despair can be removed by casting a Remove Curse spell or by using a Greater Restoration spell.

Background:

The dagger Despair was once owned by a thief named Stalker. Stalker was a skilled and ruthless assassin, and he used Despair to great effect. His victims were always filled with a sense of hopelessness and despair before they were killed.
One day, Stalker was caught by the town guards. He was outnumbered and outmatched, but he managed to escape using Despair. He killed several guards in the process, and the sight of their terrified faces filled him with joy.
Stalker eventually disappeared, but Despair remained. It is said that the dagger is now cursed, and that anyone who uses it will be filled with the same despair that Stalker felt.