Coral Corset

Armor (medium, requires attunement, very rare)

When you wear this armor, crafted of living, magically sustained coral, your armor class is 14 + Dexterity modifier (max 2). You are considered proficient with this armor even if you lack proficiency in medium armor. The armor weighs 12 pounds. You can hold your breath for twice as long as normal while wearing a coral corset (2 + your Constitution modifier in minutes, minimum 2 minutes).

Once per day, you can command the coral corset to grow and envelop its entire body in a living, mobile reef as an action. In this form, a coral corset is heavy armor and its weight doubles. Your AC increases to 18 and you gain disadvantage on Stealth checks (this disadvantage does not apply underwater). You are considered proficient with the armor in this form even if you lack proficiency in heavy armor. The reef armor lasts for a total of ten minutes before withering and crumbling, returning the coral corset to its normal form. You can also use an action to return the coral corset to its normal form at any time.

With the coral corset in either form, you never taking damage or contract coral scratch from brushing against or falling prone on a coral reef.

You also gain advantage on Dexterity (Stealth) and Dexterity (Acrobatics) checks when moving in and around coral reefs.

Once per day as a reaction, you can release a stinging venom into a creature that grapples you.

The creature must succeed at a DC 13 Constitution saving throw or become paralyzed for 1d4 rounds.