Mechanical Tail

Wondrous item, uncommon (requires attunement)
  This item is another creation of the eccentric Anton Spark, tinkerer extraordinaire. This mechanical tail is powered by a magic-infused steam core. Any bipedal creature can wear it on its back and, once attuned, use it as if it was born with a tail.
  While attuned to the mechanical tail you can use it to grapple a target within reach. You have + 2 bonus on Strength (Athletics) checks you make to grapple a target with this tail.
  Steam-powered Strike. As an action, you sweep your tail with wicked, steam-powered ferocity. Each creature within 5 f eet of your must succeed on a DC 13 Dexterity saving throw or take 2d8 slashing damage and be knocked prone. Roll a d4; on a 1 the tail runs out of steam and can’t be used again until after you finish a short rest.
  Rare variant: Increase the bonus to Strength (Athletics) checks to + 3; and change Steam-powered strike’s DC to 15 and its damage to 3d8.
  Very rare variant: Increase the bonus to Strength (Athletics) checks to + 4; and change Steam powered strike’s DC to 16 and its damage to 4d8.
  Legendary variant: Increase the bonus to Strength (Athletics) checks to +6, and change Steam powered strike’s DC to 17 and its damage to 5d10.