The best way to think about this is that
chance at finding a Tier 21+ Nightmare Sigil Diablo IV Gold . Complete that Sigil’s corresponding dungeon and you’ll unlock the crafting quest.
The third and final option only works if you have high-level friends, but it’s easily the fastest option. Join a friend who already has Nightmare Sigil crafting unlocked and help them complete a Tier 3+ Nightmare Dungeon. Even if it’s not your Sigil that was used, you’ll still unlock the crafting quest.
HOW TO USE NIGHTMARE SIGIL CRAFTING TO REACH HIGHER NIGHTMARE DUNGEONS
Once you’ve unlocked Nightmare Sigil crafting, you’ll have two new options at the Occultist: Craft Sigils and Salvage Sigils.
Let’s start with Salvage Sigils, as it’s the simplest. This works just like salvaging gear at the Blacksmith, but it’s only for Nightmare Sigils that you don’t want. Salvaging Sigils will turn them into Sigil Powder, which you’ll need for crafting.
The Craft Sigils menu looks very complex, but is actually one of the simpler crafting systems in the game. You’ll be able to craft Sacred Nightmare Sigils up to Tier 20 and then Ancestral Sigils up to Tier 100. The best way to think about this is that Sacred Sigils are for World Tier 3 players and Ancestral Sigils are for the wide range of World Tier 4 players.
Each Tier of Sigil creates a more powerful Nightmare Dungeon (which gives more Glyph XP and better rewards upon completion) and also costs more Sigil Powder to craft.
If you need more Sigil Powder, your best bet is to run Nightmare Dungeons. Nightmare Sigils can drop in Nightmare Dungeons, and will have a similar tier level to the dungeon you found them in. If you somehow run out of Nightmare Sigils, you can get more by completing Grim Favors for Diablo IV Items the Tree of Whispers.