While there is disagreement about whether this feature was part of the pre-Season or not, there is something that players have recently discovered – the Blacksmith can Salvage Nightmare Dungeon Sigils.
Dungeon Side Quest List Target-Farm Seasonal Uniques
In the comment thread, it was suggested that the Blacksmith is able to Salvage Nightmare Dungeon Sigils even before players have unlocked the Occultist.
