Frostbringer

The Frostbringer can be acquired in dungeon Doom.

It is one of many Doom Artifacts that can be acquired by defeating next creatures: The base chance of achieving an artifact is about one in a thousand (or one in a hundred from Dark Fathers). These odds improve as you make more and more kills until such time as you receive an item, at which point the counter resets.
 * Dark Fathers
 * Darknight Creepers
 * Fleshrenderers
 * Impalers
 * Shadow Knights
 * Abyssmal Horrors

They are not looted, but instead placed directly in your Backpack (or Bank Box, should you be overweight) with the following system message:

"For your valor in combating the fallen creature, a special artifact has been bestowed upon you."