Following a European Content Creator Q&A session with Game Director Ion Hazzikostas, MrGM revealed over Twitter that previously removed weapon and armor appearances will be reintroduced as transmog options in future game updates! However, it seems that the highly coveted Corrupted Ashbringer will not be one of them. While we don't yet know exactly what styles could be returning, there are many fan-favorite appearances from early expansions that are still in high demand today.
Tier 3 sets like Dreadnaught's Battlegear are still obtainable through the Black Market Auction House, but each piece can go for hundreds of thousands of gold, due to how sought after they are. Mists of Pandaria and Warlords of Draenor Challenge Mode appearances are also commonly requested, although Blizzard has often been wary of reintroducing previously hard to earn rewards.
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