Breastplate of Sunken King

Armor (any medium or heavy), very rare (requires attunement)
  When donning this armor, you hear the faint rumble of distant thundering waves as it passes over your head. While you wear this armor you gain the following effects:
  • You can understand and speak abyssal;
  • You can breathe water;
  • You can’t float in water and instead sink at a rate of 60 feet per round. Walking on the bed of a water body is not difficult terrain for you.
  Sunken King’s Favour. As an action you can cast Bigby’s Hand without any components. When cast in this way, the spell is modified as follows:
  • The hand takes the form of two Medium spectral tentacles, sprouting from the shoulders of the Breastplate. They occupy your space and move with you.
  • The reach of ‘Clenched Fist’, ‘Forceful Hand’ and ‘Grasping Hand’ is increased to 15 feet
  • ‘Interposing Hand’ can only be used on yourself.
  • You can maintain two of the spell’s effects simultaneously (e.g. use Clenched Fist while you have a target grappled with Grasping Hand), but can only command one of the tentacles with your bonus action each turn.
  The attack roll modifier for ‘Clenched Fist’ equals 4 plus your proficiency bonus. Once you use this property, you can’t do so again until the armor spends 8 hours submerged in water.
  Legendary variant: You gain a +2 bonus to AC.