Matrix Catalyst

While Season 2 of The War Within has brought us a Goblin mine cart full of new fashions to show off, it also unlocked a quick and easy path to collecting the tier sets from last season's Nerub-ar Palace raid.

It will probably not surprise World of Warcraft players to learn that The War Within once again has a new entry in the series of Catalysts -- the machines left behind by cosmic forces that allow us to convert appropriate gear into tier sets, making it much easier to obtain sets (whether for actual power gains during the season they're relevant, or for transmog after the fact).