In Scourge, you'll implant a Blood Crucible into your body, a device that is activated via gathering enough monster blood to fill it. Once you activate it, you'll be able to travel to a parallel Wraeclast. The longer you're in this apocalyptic setting, the more damage you'll take, so you'll have to keep track of the time you spend fighting The Scourge, demons that have overtaken the place.
The Blood Crucible has more than one trick though, with items you can insert in order to absorb from when you kill Scourge too. Once you have filled it in there, it will transform and give you two modifiers - one positive and one negative. Some mods may do things like raise the requirements of an item by a lot, create stat debuffs, turn off certain damage capabilities and more. While good mods can help you in various ways. The challenge will be, once again, a matter of balance and time.
You'll also be able to scourge and transform your equipment up to three times if you want to take the chance of getting better mods and a more effective balance. There are also a ton of Tainted items that will help you modify corrupted items. While you spend time battling Scourge, if you do it effectively, you'll also be able to level up your Blood Crucible. This will give you passive skill points to specialize with, opening up new paths for your characters via a good old fashioned demon slaying party.
The Blood Crucible has another surprise too -- you can place maps in it. Maps will absorb corruption and transform similarly to equipment, with a positive and negative effect. Yet corrupting your maps this way can also affect Scourge on that map overall in different ways. it might help you or it might make it a huge nightmare.
Path of Exile: Scourge will be out on October 22nd on PC and October 27th for consoles.