Purple Wyrmfist

Wondrous item, rare (requires attunement)
  From the striking violet chitin of the subterranean purple worm is crafted this surprisingly tactile gauntlet. Each day, the gauntlet produces a diluted version of the worm’s toxin that is able to cause debilitating pain through a single touch. Purple worm chitin is a sound enhancer, able to amplify vibrations and grant its wearer the ability to detect the slightest tremor.
  Purple Poison. As a bonus action you can cause the gauntlet to secrete a purple worm toxin. The next time you hit a creature with an unarmed strike, or successfully grapple a creature, the creature must make a DC 15 Constitution saving throw, taking 6d6 poison damage on a failure, or half as much damage on a success. After you activate this property, roll a d6. On a 1 or 2 you can’t activate this property again until the following dawn.
  Tactile Touch. As an action you can touch the ground with this gauntlet and gain tremorsense out to a radius of 30 feet for as long as you remain in contact with the ground.
  Uncommon variant: Decrease the DC to 13, the damage to 4d6, and the activation d6 to a d4. Remove the Tactile Touch property.
  Very rare variant: Increase the DC to 16, the damage to 8d6, the activation d6 to a d8, and the tremorsense radius to 60 feet.
  Legendary variant: Increase the DC to 17, the damage to 10d6, the activation d6 to a d10, and the tremorsense radius to 90 feet.