To play Mortal Empires, you must download it manually from Steam.
To play Mortal Empires, you must own both Total War: Warhammer and Total War: Warhammer II. But other than that, it's free. You do not need to have the first game installed.
In Mortal Empires, you can play as any lord/faction from the first game or second game, including any paid or free DLC you own. There is over 50 playable legendary lords, most of which have their own unique start location and faction.
Mortal Empires combines the Old World with the New World landmasses seen in the Eye of the Vortex campaign. The campaign features over 120 factions spread across more than 300 settlements, over 100 spells and over 350 unit types, making it the single largest campaign map ever created by Creative Assembly.
Some things have been updated and changed, compared to Total War: Warhammer. Some factions may have different names, starting positions or game mechanics. Some parts of the map are different.
Mortal Empires was originally supposed to be available on the release of Total War: Warhammer II (September 28, 2017). It ended up being released on October 26, 2017 with the Mortal Empires update.
Norsca was not playable in Mortal Empires when the campaign first released. Due to complications in development, Creative Assembly was unable to easily merge them in like the other races, and had to re-code them from scratch.
In May 2018, 7 months after Mortal Empires was released, Norsca were finally added in the Resurgent Update.
In the Potion of Speed Update Mortal Empires turn times reduced greatly, they had previously been quite long.
Provinces and factions
Map with starting locations by reddit user Henite, accurate as of the Potion of Speed update.