Harmonious Lash

Weapon (whip), legendary

This weapon functions as a +6 whip. It is a coil of alloy constructed from an unknown metal and lined with barbed spikes. Damage from the lash does not heal normally. Wounds can be healed magically but only by a wish or a heal spell. No other form of magical healing (cure spells, potions, and so on) works.

As a bonus action, you can speak a command word causing the lash to drip a powerful and debilitating venom. A creature hit by the venomous lash must succeed on a DC 18 Constitution saving throw or take 55 (10d10) poison damage. One minute later, a new save must be made (same DC) to avoid another 55 (10d10) poison damage. This damage also can only be healed with a wish or a heal spell. A creature hit by the whip must succeed on a DC 16 Dexterity saving throw or be grappled by it. The creature must use an action and succeed on a DC 18 Strength (Athletics) or Dexterity (Acrobatics) check to escape.

The first time a non-n’gathau wields the lash the character immediately takes 14 (4d6) slashing damage from hundreds of cuts and slices that appear as if the creature is being cut by a thousand invisible razors. Each time thereafter the character uses or attempts to use the lash, the character takes 7 (2d6) slashing damage from cuts and slices.