Sword of the Unicorn Slayer

You gain a +1 bonus to attack rolls with this magic weapon. Whenever you hit a fey or celestial with it, the fey or celestial takes an extra 3d6 necrotic damage. Whenever you hit a unicorn with this magic weapon, it must succeed on a DC 20 Constitution saving throw or they die instantly.
Curse. This sword is cursed, and being attuned to it extends the curse to you. While attuned to the sword, you gain the character flaw "I really hate cute things".