Path of Exile will soon be getting its biggest expansion yet - The Fall of Oriath. Once it arrives the expansion will bring with it six new acts, thus completely removing the need for multiple difficulty levels and constant replaying of the same few zones, as well as a whole bunch of new enemies (including the damnable Bonewheel Skeletons from Dark Souls), spells, bosses, and the list goes on for quite a long while.
As is tradition with pretty much any major Path of Exile update, there will also be a brand new Challenge League for everyone to enjoy in both Softcore and Hardcore variants. The league in question is simply called "The Harbinger Challenge League", and as you might expect from the name alone you will be spending a whole lot of time fighting the new and mysterious Harbingers.
Unlike the usual elite monsters the Harbingers are capable of not only creating and commanding monsters from the nearby area, but also empowering them with complementing abilities to create some truly nasty encounters. The Harbingers themselves cannot be harmed directly and can only be damaged by killing their minions, so while you're trying to deal with a whole bunch of super-empowered cannibals you'll also have to watch out for the Harbinger as it dashes all over the battlefield, constantly working to disrupt your plans.
Naturally, the more difficult a foe the better the loot, and the same applies here. Since the Harbingers are incredibly powerful they will be dropping shards of various currencies (including the high-tier ones), as well as the brand new Orb of Horizon currency item that lets you reroll a map's type to a different one of the same tier. Its not just the currency items that come in pieces, however, as the Harbinger Uniques themselves will need to be assembled before they have any sort of power. On the positive side, if you do manage to construct one of the new unique items you will be able to command your own Harbinger that can empower you in combat!
There are a few more tidbits and rewards I haven't gone over, so if you're interested in all of the details I would suggest you head over to the official website. If you would just like to give it a try for yourself, you'll be glad to hear that you won't have to wait for very long as The Fall of Oriath and its accompanying Harbinger Challenge League will be coming this August 4th.