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.
The experience curve is adjusted to make it faster than ever to prepare for the newest challenges, and each level along the way will provide more meaningful increases in progress and power. All expansion zones are getting more flexible, too; they'll be able* to scale to you and your friends while you level to 50, so it's easy to try a zone you've never played.
Blizzard started testing World of Warcraft: Shadowlands last week, and is slowly allowing players in to test new zones and features. While the “Adventures” mission table isn’t available on the test realm yet, we should see some version of it pop up in the next few months. Whether it actually turns out to be an autobattler or not remains to be seen.
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 Realm of Shadows may be the same World of Shadows as the one that becomes visible when a [Elixir of Shadows] is consumed. It may also have something to do with shadow magic and shades. Death knights, necromancers, and undead as a whole share a strong connection with the Realm of Shadows from many hints that can be seen in-game. In the death knight starting zone, death knights are given the task to enter the Realm of Shadows in order to gain their Deathcharger. Later on, death knights are eventually able to learn the ability [Raise Ally] which pulls their ally's spirit back from the Realm of the Dead and forces it back into their body. Upon doing so, a buff is applied to the player stating that: "A touch of the spirit realm still lingers..." This shows that death knights and necromancers both have a connection to the Realm of the Shadows/Dead to perform necromancy which furthers the idea that they actually are drawing their magical power from it.
The popular autobattler mode (games like Teamfight Tactics, Dota Underlords, and Blizzard’s own Hearthstone Battlegrounds) lets players draft units and place them on a chess-like board. The units then battle the units of another player. Between battles, players can buy new units, upgrade existing units, or rearrange them on the board. And according to Shadowlands’ most recent datamine on MMO Champion, World of Warcraft is getting a similar mode.
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.
Sometimes enemies will drop Phantasma, a currency that is unique to Torghast. You may also find Phantasma from Anima Powers or breakable objects. Your Phantasma all disappears as soon as you leave Torghast. Occasionally, you may find a Broker, a Phantasma vendor within Torghast, who will allow you to spend your Phantasma to buy Anima Powers, along with other consumables that will aid you on your run.
Shadowy Tormentors inhabit this dimension, and emerge from it to torment death knights such as Koltira Deathweaver. The Lich King originally kept them at bay, but after the Knights of the Ebon Blade left his service, the tormentors are now loose upon them. He even appears in the World of the Dead, as he calls it, riding a frost wyrm during  The Power to Destroy.