In the opening cinematic, Sylvanas shatters the Helm of Dominion, breaching the veil between the material realm and the Shadowlands, an ancient dimension where the dead coalesces for judgment. Sylvanas' actions have upset the natural balance between life and death, and it's on players to enter the Shadowlands itself and repair the cycle before it is too late.
For the first time since the release of World of Warcraft in 2004, Shadowlands will involve a level reduction ("level squish"), with player characters at level 120 (the level cap in Battle for Azeroth) reduced to level 50, with level 60 being the new level cap (as it had been in the original game). In what Blizzard has called a "New Game+ experience", newly-created characters will have an updated starting experience on an island called "Exile's Reach", which will introduce them to the game and its systems. For players new to World of Warcraft, characters who finish the starting experience on Exile's Reach will proceed to Battle for Azeroth content, while veteran players who create new characters can choose the expansion experience they wish to play through to level 50, at which point they would proceed to the Shadowlands.
The four zones that comprise the Shadowlands are ruled by "Covenants", similar to the Class Orders introduced in Legion. Each Covenant will have its own campaign, similar to the War Campaign in Battle for Azeroth, with gear specific to the faction and abilities both universal and determined by class. The four covenants are the Kyrian of Bastion, the Night Fae of Ardenweald, the Venthyr of Revendreth, and the Necrolords of Maldraxxus. Players experiencing the Shadowlands content for the first time will need to reach level 60 before they can choose to pledge themselves to a Covenant, while alts are able to do so at the start of the Shadowlands content.
Adventurers entering the Shadowlands will find the realm of the dead in disarray. In the natural order of things, souls are sorted and sent on to an afterlife realm appropriate to the lives they lived, but starting around the time of the Burning Legion's third invasion of Azeroth, all souls who have perished—including the innocents slain at Teldrassil—are being funneled directly into the Maw. The Shadowlands are starving for anima even as the Maw continues to grow from the glut of fresh souls. Sylvanas Windrunner has been seemingly perpetrating acts to bring about great amounts of death and destruction. In partnership with the Jailer, they have been working toward a common end for some time.
The Shadowlands will feature five major zones - Bastion, Ardenweald, Revendreth, Maldraxxus, and the Maw. In the center will be the city of Oribos, which functions as the main player hub similar to Shattrath City in Outland in The Burning Crusade or Dalaran in Wrath of the Lich King and Legion. There will be four new dungeons for leveling, four more at maximum level, and a new raid. In addition, a new roguelike "endless dungeon" called Torghast, Tower of the Damned, will be introduced for both solo and group play.
Spirit healers decide when it's time for a mortal soul to pass into the Shadowlands. When a mortal dies and their soul crosses the veil between life and death, it is shepherded by the kyrian to Oribos so that they can be judged by the impassive Arbiter. All of the soul's contents—deeds, misdeeds, thoughts, accomplishments, and failures—are instantly laid bare before the Arbiter, who then judges in a mere instant and sends the soul off to one of the infinite realms of the Shadowlands, each of which is ruled over by a powerful Covenant. The Covenants are ancient and powerful orders who have existed since the Shadowlands were shaped long ago, and who bear sacred duties to help maintain the afterlife's ecosystem. Not every soul is filtered into the main four Covenants. Each soul brings with it a vital force known as anima, the product of all of the soul's experiences and actions in life. Anima is the lifeblood of the Shadowlands, making trees grow and rivers flow and is the source that's drawn upon to conduct the magic of death. Great souls—both good and evil—have a lot of anima, while those who have lived humbler lives have less. Four of the realms—Ardenweald, Bastion, Maldraxxus, and Revendreth—are especially vital to the functioning of the Shadowlands. However, there could be infinite afterlives, some small and tailored to a single person while others are vast and full of either splendor or torment. Between each realm is a cloudy space which was once rich with streams of anima connecting the different domains, but the current anima drought has caused the realms to become cut off from one another, breeding fear and mistrust among the inhabitants.