Sharkskin Vest

Armor (leather), rare (requires attunement)

While wearing this armor, you gain a +1 bonus to AC, and you have advantage on Strength (Athletics) checks made to swim.

While wearing this armor underwater, you can use an action to cast polymorph on yourself, transforming into a reef shark. While you are in the form of the reef shark, you retain your Intelligence, Wisdom, and Charisma scores. In addition, you don’t need to maintain concentration on the spell, and the transformation lasts for 1 hour, until you use a bonus action to revert to your normal form, or until you drop to 0 hit points or die. The armor can’t be used this way again until the next dawn.