As you might already know, Echoes of the Atlas came with a new villain called The Maven. Fighting it will reward you with the new Atlas passive abilities, Waystones, and more powerful rewards such as the Maven's Orb.
To find her, you must first get noticed by her. How? You might ask. You need to find The Envoy. This NPC appears randomly on any map. When you find him, you must keep in touch four more times. At that point, The Envoy will mention that The Maven will be observing you. After you defeat the map Boss, The Maven will drop a beacon called The Maven's Beacon.
Go back to your hideout and add the item to your map device. The device will be permanently upgraded, giving you the liberty of summoning The Maven from anywhere. Head to any of the high-rank maps; you will see that a button will appear, giving you the option of calling The Maven. Complete the map for her to be pleased. Repeat on different high-rank maps until you receive the invitation.
The invitation is a map fragment that can be added to your map device, opening six portals that lead to The Maven's Crucible. Go through any of them and get ready to fight the bosses you defeated. There is a catch; they are enhanced. Defeating them inside the Crucible will grant you the Maven's Gift that can be used on your Atlas passive tree.
Remember to put on your best gear before start The Maven's trial. Best of luck!