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.
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.
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 were originally intended to be a fully playable zone in World of Warcraft, designed for high-level play. The idea was that as deceased characters made their way back to their corpses, they'd see high-level players battling creeps in the area, which would inspire lower level players to increase their character level so they could experience the zone for themselves.
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.