Amulet of the Coldfire Phoenix

Wondrous item, very rare

A blue pendant in the shape of a phoenix clutching a shimmering blue orb hangs from this leather cord. While wearing the necklace, you you gain resistance to cold damage, but vulnerability to fire damage.

In addition, when you are reduced to 0 hit points while wearing the necklace but not killed outright, you can drop to 1 hit point instead. When you do, you gain 100 temporary hit points. If a creature hits you with a melee attack while you have these hit points, that creature takes 25 cold damage. Once this property has been used, it can't be used again until 3 days have passed.

"I fear not the fires of Hell but the cold loneliness that death may bring."