There might be other ways to obtain this item, but it might not be ever available again.
After a long battle with an enraged Yeti, the survivors were all but tired, cold and well... dying. All the chests looked exactly the same. One such survivor, however, found the courage to continue, to find a chest, so frozen that only his fiery soul could thaw it out. To his disappointment, all he found was a downsized version of the very weapon that had slaughtered many of his comrades, but this legend of the chest continued to be passed down in the stories of every winter to come.
- Try to not be near the centre of the arena after beating the boss, as you may be forced to waste your time unlocking a regular chest.