Crab Plate

Armor (Breastplate, Half Plate, Spint Armor, or Plate Armor), Very Rare (Requires Attunement)
Appearing as a polished mithril breastplate fashioned to mimic a giant crab with legs wrapping around the torso of the wearer.
While wearing this armor, you have a +1 bonus to Armor Class, are immune to the stunned and restrained conditions, and can breathe in water.
In addition, whenever you have the unconscious condition or have died, the breastplate immediately animates becoming a Giant Crab (use the entry in the Monster Manual with the following changes: 16 AC and 40 HP). This crab seeks to protect your body from all harm until you regain consciousness or it is slain, at which point it reverts to its dormant breastplate state. While the crab is within 5 feet of your body, attacks targeting you do not gain the advantage or automatic critical hit benefits of your unconscious condition. The crab can move at its normal speed while carrying your body. The crab cannot communicate, but will only attack or interfere with the actions of hostile creatures.