Amulet of Invulnerability (cold)

While you wear this amulet, you have resistance to cold damage. Additionally, you can use an action to grasp this amulet in your hand and magically become immune to cold damage until the end of your next turn or until you are no longer wearing the amulet. When you use this special action, until the end of your next turn, your movement speed is 0. In addition, for this duration, at the beginning and end of each of your turns, any creature within a 5ft radius of you must succeed on a DC 8 Constitution saving throw or be grappled and unable to use its limbs. Once this special action is used, it can't be used again until the next dawn.

Notes: Resistance: Cold, Immunity: Cold, Combat, Warding