Before the Fall of Oriath update, Path of Exile had four acts which were then repeated twice with slightly higher difficulty. Acts are what split the areas of the game and the story up, similar to a level in a more linear game or a chapter in a book.
Not only does the update add a fifth act, in which you return to Oriath where your character originally comes from, but the structure afterwards also saw some changes. Five new acts replace the cruel and merciless difficulty versions of acts, and while some of the general areas and important locations are used, there are a lot of new areas that you will have to explore. Rather than playing through the story three times, you’re going from start to finish once.
The Pantheon is a new system introduced in the second half of the game that lets players give an extra boost to the stats of their character in some way. These boosts that can be activated only become available when you defeat bosses known as gods from the sixth act onwards.
There are four major gods and seven minor gods that you can choose from, and you can have one power from each pool activated at one time. These can also be changed for free in a town. Each power gives you something different. For example, the Soul of Lunaris is a major god power that increases your physical damage reduction and movement speed for each enemy up to a maximum limit.
Path of Exile has had challenge leagues in the game for the last four years. They are different to a standard league in that they start with a separate economy and a fresh start, while they also have at least one new gameplay mechanic specific to that league.
With the arrival of the Fall of Oriath update, the developers have retired the Legacy league and it has been replaced with the Harbinger league. Available in both standard and hardcore variants, in the league there is the potential for a Harbinger enemy to spawn which you can only kill by defeating the mobs that it spawns. There are also 40 optional challenges that you can choose to complete, which range from defeating a Harbinger to identifying 100 unique items.