Sea-Serpent's Coil is a Mythic ring item which is obtainable for players who own the High Isle expansion. 

To obtain Sea-Serpent's Coil, you will need to find five leads. When you have found them all, the item will automatically construct itself in the highest quality. 

Sea-Serpent's Coil gives you 40% damage reduction when you are at full health, and when you take damage you instead get extra damage output at the cost of a movement speed reduction. Note that the damage output increase comes via the Major Courage and Major Berserk buffs, so if you already have those buffs from another source then it's probably not worth wearing this Mythic Item.

Sea-Serpent's Coil visual effectIn order to start the process of obtaining Sea-Serpent's Coil, you will need to have access to the Greymoor DLC, either by owning it or by having an active ESO Plus subscription. You also need to have the Excavation and Scrying skill lines at at least rank 7 in order to scry and dig for master level leads. If you're not sure how Antiquities work, then check our Antiquities Guide, which will explain the process to you. You will need to get the following leads in order to construct Sea-Serpent's Coil: