Patch 8.3 introduces Corruption to the Raid Crafting Gear from Tailoring, Leatherworking and Blacksmithing, adding a Tier 3 Secondary Stat Positive Affix to these pieces of all item levels, but also adding +25 Corruption. You'll also need a Void Focus to craft it, which will probably work similar to the Abyssal Focus from Nazjatar. Once you craft the 440 version, it'll unlock the 455 version, and crafting that will unlock the 470 version. We're not exactly sure what that means, but it'll likely drop from the N'zoth invasions in Uldum and Vale of Eternal Blossoms. The drop for the base 440 item level pieces are N'zoth Cultists. These items also come with a guaranteed socket and random secondary stat rolls. Both these pieces will also be offered at 3 item levels, and for Season 4, those item levels are 440, 455, 470, 5 item levels lower than the Normal, Heroic and Mythic raid item levels respectively. Similar to every other tier in Battle for Azeroth, the Season 4 Crafted Raid Gear will come in two gear slots (depending on the profession).

This comes after another change to add Corrupted Weapons. This is no longer the case and has been removed in a future PTR build.

Wow bfa dredged leather