Fullmetal Cloak (5e Equipment)
From D&D Wiki
Armor (plate), rare (requires attunement)
This armor has two forms it can switch between using a bonus action. Due to its animated design, if you have proficiency in light armor, you are also treated as having proficiency in heavy armor while wearing this cloak, and you do not have disadvantage on stealth checks.
Cloak mode: The armor wraps loosely around your body, like a cloak made of metal plates. It lashes out at attacks that would hit you. When you would be attacked by a ranged attack, you may use a reaction to increase your AC against the attack by 4. The cloak can also slow your descent, allowing you to use a reaction to reduce fall damage by 20.
Carapace mode: The armor wraps tightly around you, turning into an armored carapace. You are given an additional +1 to AC. Your land speed increases by 10 feet, and your jump height and distance are doubled.