according to wowhead the pattern for this Pattern: Shadoweave Mask - Item - World of Warcraft says "This item's source is no longer available/removed" but according to one comment it should drop from Dark Iron Steamsmith - NPC - World of Warcraft but i havent seen it personally and it dosent show up on wowhead.
but this specific item should be used for a mount that was added in patch 7.3 which is Lucid Nightmare - Item - World of Warcraft
i have crafted this item and sold quite a few of them and atm on my server they sell for minimum 50k each so hopefully others can get some gold from it aswell.