Blizzard celebrated the 11th Anniversary of World of Warcraft from November 16 through November 30, 2015. Players who logged in during that time received several collectible gifts.
I haven’t taken the time to play around with all of them, but immediately equipped the Inflatable Thunderfury, Blessed Blade of the Windseeker. I managed to get it on all of my characters, except my Pandaren (because I couldn’t find a mailbox near him.) The screenshots you see in this blog were taken on November 16, 2015.