Ring of Cold Vengeance

Ring, very rare (requires attunement)

This delicate band of polished sapphire and silver is engraved with cruel fangs. When a creature hits you with a melee attack while you are wearing the ring, you deal an extra 1d6 cold damage the next time you hit that foe.

This extra damage increases by 1d6 for each subsequent hit you take from that attacker, up to a maximum of 5d6 cold damage. These bonus damage dice disappear after 1 minute if you do not strike your attacker in melee.

Rather than attacking with a weapon, you can instead make a melee spell attack with the hand wearing the ring of cold vengeance. A successful hit deals your unarmed strike damage plus the cold damage described above, and in addition, the target must make a DC 15 Strength saving throw or be coated in ice and restrained.

A restrained creature can make a new saving throw each round at the end of its next turn and takes an additional 1d6 cold damage each round it remains restrained.

Curse. This ring is cursed and becoming attuned to it extends the curse to you. As long as you remain cursed, you are unwilling to part with the ring, wearing it at all times, and you have disadvantage on saving throws against fire.