As asked, some ideas to KHAZAD
Theme: Slow player.
Flavor: A dwarf realm which is praises highly tradition and religion. These two aspects are mixed in their cult of the ancients leaded by the stonespeakers. This cult values highly also the earth which envelops their subterran cities. This love for tradition enabled them to preserve some old knoledge from the Age of Magic: Gunpowder.
Gameplay:
Military: Strong defender, but their units are slow, so must plan before is attacked or he will be outmaneuvered. The underdark is a way to move their units between th cities without them be catched in the open, but it is not a Obsidian Gate, the units take some to arrive in it's destination, so cannot be used to answer a attack which is already happenning. The underdark can be used to send away important units.
In the offense they are great mid to late game siegers, but bad open spaces skirmishes. Their slowness and lack of roads give the enemy a lot of time to prepare their defenses.
Unique Mechanics:
Underdark Expedition (power): This power can only be used in a city with a Underdark Entrance. The player target a city with another Underdark Entrance. Removes the selected units from the game and a number of turns later, proportionally to the distance between the cities. It is the dwarven way to travel. (based in Corlindale idea)
Subterran City (city trait): Improvments in the city big cross cannot be pillaged and are invisible. The player should be able to see it. There is a problem to represent it. The city provides +25% to it's defenders. Improvments can be destroyed by the Earthquake spell.
Honor (promotion): When the unit attacks, it gains +40% in combat. It gains -20% per level difference if the enemy's level is lower than the unit. This reduction doesn't happen when fighting against heroes.
Clans (building trait): Each Clan Hall build normally provides a bonus for each hall of the same guild across the realm or the world. The cost to build each guild hall increases proportionally to the number of halls of this guild in the world, because of logistics problems.
Cold Rage (power): Calls the spirit of a furius ancient warrior which possesses the battlerager. Gives +40% to attack and -40% to defense until the start of your next turn.
Long-range Artillery (power): Create a powerful cannon ball with two movement and high power.
Siege Weaponry (power): All the units in the stack gain city raider until the end of the turn. It builds in place siege towers, battering rams and explosives.
Vessel of the Ancients (power): Any unit in a city with a Stonespeaker Clan Hall can use this power. The unit gains permanently the Vessel of the Ancients promotion. It1s movement becomes 0, and he gains +5% in combat times the pop level of the city.
Unique Units:
Deepwarden (Ranger): Have the Underdark Expedition power.
Earth Dreamer (Mage): A disciple. Can only acess all Spirit and Earth spells level II, sorcery, summoning and divine.
Stonespeaker Guardian (Archmage): Upgraded Earth Dreamer. Acess to level III spells.
Battlerager (Berserk): Can use the Cold Rage power.
Big Bertha: Can be captured by the enemy. It is immobile. Has the Long-range artillery power. Is build only by the Siegemaster. Can only so many Bertha as Siegemaster.
Siegemaster (National Unit: 5): Can be captured by the enemy. Can build Big Bertha, but it takes few turns. Has also the Siege Weaponry power.
Thunderer (Flurry): Dwarf with two pistols. Archer with blitz.
Dwarven Sniper (Marksmen): Marksman renamed.
Flame Cannon: High collateral damage siege unit, fights SOD instead of the Fire Mages.
Unique Buildings:
Underdark Entrance: Allow the use of the Underdark Expedition power.
Dwarven Beer Secret Recipe (World Wonder): Generates 3 Dwarven Beer resouces.
Gearfinger Clan Hall (Clan) (Archery Rande and Sige Workshop): Build archer and siege units. When the city is lost to the enemy you can chose to destroy the city. Well places gunpowder barrels make the uderground city collapses. The population escapes and the enemy gets one dwarven slave for each pop point of the city.
Redbeard Clan Hall (Clan) (Barracks): Produces the same units as Barracks. The units starts with +1 xp per Redbeard Guild Hall in the Realm.
Metalhugger Clan Hall (Clan): Increases the city hammer production by 1 per city with a Metalhugger Clan in the world.
Stonespeaker Clan Hall (Clan) (Elder Coucil): Can build Earth Dreamer. Reduces the maintence by 10% per Stonespeaker Clan Hall in the world.
Spellrazor: A magic weave created with spirit and fire by the local Stonespekers to protect the city from the Khazad's enemies black magic. Whenever a unit uses a spell in the citie's big cross it receives damage. Needs a Stonespeaker clan in the city to be build. Units casting spells from the city are not affected. Generates 1 Happiness, the population feels safer.
Sentinel Barracks: All units build starts with city guard. Need a Redbeard Clan Hall to be build.
Siegemaster Academy (National Wonder): Can build Siegemaster. Can only be build if you control 4 or more Gearfinder Guild Hall.
Hold Entrance: Palisade renamed.
Perimeter Defense: City walls renamed.
Dwavern Fortress: Castle renamed.
Twists:
All cities start with the subterran trait.
The Khazad have no cavalry.
Cannot build road, use the Underdark to move.
Their leaders do not accept treats easily, but when they accept they hardly breaks them.
No normal adepts.