The Spiked Armor can be found in Sword Coast Adventurer’s Guide, page 121.
While wearing this armor, you have a swimming speed equal to your walking speed. In addition, whenever you start your turn underwater with 0 hit points, the armor causes you to rise 60 feet toward the surface. The armor is decorated with fish and shell motifs.
Spiked armor is a rare type of medium armor made by dwarves. It consists of a leather coat and leggings covered with spikes that are usually made of metal.
The wearer has Disadvantage on Dexterity (Stealth) checks.