The Misty Mountains is a yet to be released faction. It is a very diverse faction, divided into three different realms: Moria, Goblintown and Gundabad. Its game style is aggressive and focused on horde tactics. The starting fortress is the largest realm, Moria, and offers only 4 building plots with few available building options. Unlike other factions, however, the Misty Mountains can recruit pioneers who can free-dig anywhere on the map to the different realms. On camp maps, the start fortress is equipped with 3 building plots.
The units of the Misty Mountains vary according the realm and offer different strengths and weaknesses. Each realm is represented by a specific hero, who emphasises certain elements thereof. On settlements, wild creatures like Dragons and Giants can be recruited.
The Misty Mountains has not been released yet but is an upcoming faction of Evil. The faction was initially the Goblin faction in BFME 2, but it has been divided into three sub-factions and then regrouped into a single one again.
News of Misty Mountains
So far, the only news the Edain Team has released about the Misty Mountains faction is from the original 'The Road to Edain 4.0' articles. More news will be released closer to the release of the faction. The articles below are old, so it is reasonable to expect that there might be additional changes to the finished product.
http://www.moddb.com/mods/edain-mod/news/the-road-to-edain-40-misty-mountains-part-one - basic information about buildings, porters and goblin realms.
http://www.moddb.com/mods/edain-mod/news/the-road-to-edain-40-misty-mountains-part-two - information about units, heroes and spellbook.
https://www.moddb.com/mods/edain-mod/news/the-road-to-edain-40-of-trolls-and-army-commanders - information on heroes of the misty mountains
The Edain Team has decided that Moria will be the starting base for the faction and would be designed around ransacked dwarven strongholds. They have stated that Moria would provide goblin swordsmen, archers, drummers and cave trolls.
Goblin Town would be based on the design from the Hobbit films. Goblin Pillagers will steal resources by attacking enemy buildings. Sappers will be able to dig tunnels from one point to another, bypassing walls and units in the process.
Gundabad would be based aesthetically on the original Goblins faction from vanilla BFME 2. It would offer heavy infantry in the form of Gundabad Swordfighters and Pikemen, as well as cavalry in the form of Warg Riders. Gundabad would also be the only goblin realm with Sentry Towers. Gundabad's unit designs are based on the hunters from An Unexpected Journey.
The Edain Team has stated that they will streamline the hero line-up by removing Shelob, Buhrdur and Drogoth. Shelob was removed along with all other spiders, while Buhrdur and Drogoth were removed for being made up and having similar roles to each other and Smaug (mass-slaying).
The old Coronation System (when one hero could be crowned as king of the Goblins) was removed. Instead, only Bolg would have that role and therefore have his own name (instead of a title) among the Goblin Heroes. All other heroes would just have titles and descriptions instead of names. Bolg will be the faction leader and unifier of all goblins.
Each separate realm would have its own leader. Goblin Town would be led by the Great Goblin. Moria is led by the Moria Chieftain. This hero would be the replacement of Gorkil, using his design but changing the powers to swarm the enemy and weaken monsters. Gundabad will be led by The Defiler, using the design of Azog from the Hobbit films. Since Azog's presence was a violation of the lore, the Edain Team decided to just use his title like with the other goblin heroes. He would lead the cavalry and hunt down enemy heroes.
The monsters will be represented by Tom, Bert and Bill. Bert will be controlled while Tom and Bill follow him around. They are designed to be tanks.
Smaug will be able to be recruited from the beginning and used permanently. He will also be the ring hero, though the changes that the ring will bring have not been decided. He would have the four-legged dragon design from the the first Hobbit film rather than the Wyvern design from the second and third films.