Mariner's Armor
Source: Dungeon Master's Guide
Armor (Any Light, Medium, or Heavy), Uncommon
While wearing this armor, you have a Swim Speed equal to your Speed. In addition, if you start your turn underwater with 0 Hit Points, you immediately regain 1d4 Hit Points. The armor can’t heal anyone again until the next dawn.
The armor is decorated with fish and shell motifs.