Path of Exile's Incursion league, which Steven spoke to the developers about in length last month, is now live.
Incursion has you hunt down Atzoatl, an ancient Vaal treasure temple. To reveal its location, you'll have to travel back in time to its construction. That requires you to find Alva Valai, a new NPC, who will send you back in time to a random room in the temple. There, you'll have a limited amount of time (as little as 30 seconds) to kill as many monsters as you can, with each kill granting more time. At the end of the fight, you can claim your loot.
You'll have to track down Alva Valai 11 times—she'll appear in each new area during a regular campaign—to reveal the location of Atzoatl in the present day, which you can then raid for goodies. The time-bending twist is that your actions during your 11 incursions into the past will change that final temple dungeon run. For example, finding keys and unlocking doors in the past will open up more of the temple to explore in the present.
It can get very complex, from the sounds of Steven's piece. Each room has competing 'architects' that want to design the room a certain way. Kill one architect and the other is free to do their work, changing the room and potentially impacting the rest of the temple. You can travel back to the same room more than once during your 11 incursions, giving one architect multiple chances to upgrade the room to their liking.
In Steven's run, he upgraded a poison garden multiple times, which meant poison plants covered every room in the temple, making his final run more difficult. But reaching the original poison room netted him a shield that you can't find anywhere else.
Alongside Incursion, developers Grinding Gear Games added heaps of gems, 31 new items and 22 divination cards. All the patch notes for the update can be found here. The Incursion league will run for three months.