The The Baneful is a rare magical shortsword that only functions if it's Bound to an Eldritch Knight or is a Warlock's Pact Weapon.
The wizard Otiluke wrote about bound weapons and their propensity to coalesce with their wielder as the pair come together. He also wrote about their dangers, which are manifold, and their benefits, which make the danger worth it.
Properties
- Damage
1d6 + 1 (2~7) + Strength or Dexterity modifier 
Piercing damage - Details
Shortswords 
Rarity: Rare
Enchantment: + 1
One-Handed
Finesse
Light- Dippable
Melee: 1.5 m / 5 ft
Weight: 0.9 kg / 1.8 lb
Price: 190 gp
Special
The holder of this item gains:
- Favoured Weapon: This weapon has a +1 bonus to damage and Attack Rolls
- Baneful Bond: On hit, possibly inflict Bane your target. Saving Throw DC 14.
- The warlock bound to this weapon is always Proficient with it. The weapon's damage is magical.
- The weapon uses the caster's Spellcasting Ability Modifier for
Attack rolls and damage rolls. - Prevents the weapon from being dropped or otherwise disarmed.
Weapon actions
If you have proficiency, equip in main hand to gain:
-
Flourish (
)- Feint an attack to possibly throw your opponent
.
-
Piercing Strike (
)- Stab an enemy and possibly inflict
.
Where to find
Sold by Blurg in the Myconid Colony.