This is all purely hypothetical since I have no clue how to make a mod, but for fun I decided to come up with how the four nations from Avatar could be represented as Civ factions.
The Fire Nation
Symbol: Fire Nation Emblem
Colours:
Unique Unit - Empire-Class: Unique Fire Nation naval melee unit, replacing the Ironclad. Unlike the Ironclad, the Empire-Class is unlocked by researching Mass Production rather than Steam Power, and can perform coastal raids.
Unique Infrastructure - Firebending Factory: Fire Nation unique building, replacing the Factory. Unlike the Factory, the Firebending Factory is unlocked by Mass Production instead of Industrialization, and it provides 2 Science to cities within six tiles on top of the standard 3 Production.
Leader - Sozin (Sozin's Comet): Every 100 turns, all military units gain +30 strength for 10 turns.
Leader Agenda - Shared Prosperity: Focuses heavily on maximizing the Production output of his cities. Hates civilizations whose cities are less productive than his cities, especially if they are also less technologically advanced.
Leader - Ozai (The Phoenix King): Whenever you raze a city, all other Fire Nation cities immediately gain Loyalty equal to double the razed city's Population. Pillaging or performing a Coastal Raid also pillages all adjacent tiles. (Indirectly pillaged tiles do not generate gold or health.) Gain access to the Airship unit after researching Square Rigging.
Leader Unique Unit - Airship: Air bomber unit unique to the Fire Nation when lead by Ozai, unlocked by researching Square Rigging. Requires 1 coal to train and consumes 1 coal per turn. Upgrades to a Bomber.
Leader Agenda - Fight For Your Honour: Likes civilizations that have recently won a war against a civilization other than the Fire Nation. Hates civilizations that have recently lost a war. Overall somewhat hostile by default and difficult to befriend.
Cities:
Symbol: Air Nomad Emblem
Colours: Pale blue symbol, pale grey background
Civilization Ability - The Element of Freedom: Cities other than the capital generate 1 Faith per turn for every two tiles between them and the nearest Air Nomad city, (Doubled to 2 Faith per turn after researching Theology) and gain 1 Amenities and generate 1 Great Prophet point per turn for every five tiles between them and the nearest Air Nomad city. Cannot settle new cities within ten tiles of an existing Air Nomad city. Whenever an Air Nomad military land unit is targeted by a melee attack, there is a 1/3 chance it (and any units it is escorting) will instead move backwards one tile and take no damage.
Unique Unit - Flying Bison: Unique Air Nomad Support unit, unlocked by researching Horseback Riding. Has a movement speed of 5, pays only 1 movement point per tile regardless of terrain, can travel on to water tiles without embarking, and can travel through normally impassible terrain such as mountains or ice. Any non-cavalry non-naval units in formation with a Flying Bison also gain these traits. Does not upgrade into any unit, and never becomes obsolete.
Unique Infrastructure - Air Temple: Air Nomad unique District, replacing the Holy Site. Non-military units can be airlifted to and from tiles adjacent to an Air Temple, (Military units can be airlifted as well after researching the Rapid Deployment civic.) and cities with an Air Temple exert Loyalty pressure on all other cities with an Air Temple belonging to the same civilization, regardless of distance. Additionally, the Air Temple receives a major adjacency bonus from Mountains rather than a standard adjacency bonus, and costs half the production of an ordinary Holy Site to construct.
Leader - Gyatso (Vow of Non-Violence): Unimproved sources of crabs, deer, fish, furs, ivory, and whales provide +3 faith, but do not provide food, production, or gold, and cannot be improved or harvested. Horses and sheep each provide +2 faith, but no food, and cannot be harvested. (But can be improved.)
Leader Agenda - Peaceful Wanderer: Will seek to found cities much further away than other leaders, in accordance with the Air Nomad Unique Ability. Is also very reluctant to declare war. Likes civilizations that border him, have mutual Open Borders treaties with him, or send Trade Routes to his cities. Dislikes civilizations that declare many wars.
Cities:
Symbol: Water Tribe emblem
Colours:
Unique Unit - Healer: Unique Water Tribe Support unit, unlocked by Apprenticeship. Units adjacent to a Healer heal 10 health per turn, increased to 20 health per turn if the Healer is adjacent to a lake, coast, or river. Upgrades to a Medic.
Unique Infrastructure - Igloo: Unique Water Tribe Improvement, unlocked with Masonry. Provides +1 food, +1 production, and +0.5 Housing. Food and Housing bonus is doubled if adjacent to either two (or more) Igloos or a City Center and one (or more) Igloo. Can only be built on Snow tiles.
Leader - Sokka (The Ideas Guy): Receive a free random Inspiration or Eureka (prioritizing earlier techs and civics over later ones) whenever you discover a new civilization or city-state using a naval unit. +1 Science from Fishing Boats and Igloos.
Leader Agenda - Clever Warrior: Likes civilizations with a technologically-advanced military, as long as they do not declare many wars. Dislikes civilizations with technologically-advanced militaries if they frequently declare war.
Leader - Yue (Moon Spirit): Population loss and unit damage from blizzards and floods is reduced by 75%. Population loss and unit damage from blizzards and floods is doubled for civilizations at war with the Water Tribe. The chance of a blizzard or flood occurring in Water Tribe territory is increased by 10% for every hostile military unit within Water Tribe territory. +2 Faith from Fishing Boats and Igloos.
Leader Agenda - Respect the Balance: Likes civilizations that have a high Faith output and respect the environment. Dislikes civilizations that have a low Faith output and disrespect the environment.
Cities:
Symbol: Earth Kingdom emblem
Colours:
Unique Unit - Disc-Thrower: Earth Kingdom unique ranged unit, replacing the Crossbowman. Has 55 melee strength when defending (equivalent to a Musketman.) and starts with the "Garrison" promotion, but has a range of 1.
Unique Infrastructure - Monorail: Earth Kingdom unique building which does not replace anything, is unlocked by Construction, and is constructed in the City Center. Culture generated by a city with a Monorail generates 10% more Domestic Tourism, increased to 30% more Domestic Tourism after researching Combustion, and units starting their turn in a city with a Monorail gain +2 Movement. Additionally provides 2 Housing.
Leader - Kuei (Grand Secretariat): Gain access to a unique governor: Long Feng, the Grand Secretariat. Long Feng's Titles are extremely powerful, but the city where he is established loses 4 Loyalty per turn instead of gaining 8 Loyalty per turn. Additionally gains access to the "Dai Li Agent" Unique Unit after researching Civil Service.
Leader Unique Governor - Long Feng:
Leader Agenda - Harmony Restoration Movement: Likes civilizations that do not settle cities on continents other than their home continent. Dislikes civilizations from other continents who settle cities on his home continent, and hates civilizations from other continents who conquer cities on his home continent.
Leader - Kuvira (The Great Uniter): Killing a military unit on the Earth Kingdom's home continent causes foreign cities within nine tiles to lose 10 Loyalty, and Earth Kingdom cities within nine tiles to gain 10 Loyalty. Both of these bonuses are doubled if the defeated unit is a Barbarian. +1 Science and +1 Production from mines built on copper, mercury, silver, aluminum, or iron.
Leader Agenda - New Earth Empire: Likes civilizations with capitals on other continents who wage war on civilizations and city-states on the same continent as their capital. Dislikes civilizations with territory on her home continent, regardless of the location of their capital.
Cities:
The Fire Nation
Symbol: Fire Nation Emblem
Colours:
- Grey symbol, red background (Sozin)
- Dark gold symbol, maroon background (Ozai)
Unique Unit - Empire-Class: Unique Fire Nation naval melee unit, replacing the Ironclad. Unlike the Ironclad, the Empire-Class is unlocked by researching Mass Production rather than Steam Power, and can perform coastal raids.
Unique Infrastructure - Firebending Factory: Fire Nation unique building, replacing the Factory. Unlike the Factory, the Firebending Factory is unlocked by Mass Production instead of Industrialization, and it provides 2 Science to cities within six tiles on top of the standard 3 Production.
Leader - Sozin (Sozin's Comet): Every 100 turns, all military units gain +30 strength for 10 turns.
Leader Agenda - Shared Prosperity: Focuses heavily on maximizing the Production output of his cities. Hates civilizations whose cities are less productive than his cities, especially if they are also less technologically advanced.
Leader - Ozai (The Phoenix King): Whenever you raze a city, all other Fire Nation cities immediately gain Loyalty equal to double the razed city's Population. Pillaging or performing a Coastal Raid also pillages all adjacent tiles. (Indirectly pillaged tiles do not generate gold or health.) Gain access to the Airship unit after researching Square Rigging.
Leader Unique Unit - Airship: Air bomber unit unique to the Fire Nation when lead by Ozai, unlocked by researching Square Rigging. Requires 1 coal to train and consumes 1 coal per turn. Upgrades to a Bomber.
Leader Agenda - Fight For Your Honour: Likes civilizations that have recently won a war against a civilization other than the Fire Nation. Hates civilizations that have recently lost a war. Overall somewhat hostile by default and difficult to befriend.
Cities:
- Royal Caldera City (Capital)
- Fire Fountain City
- Shu Jing
- Jang Hui
- Ember Island
- Yu Dao
- Pohuai
- Bhanti
Symbol: Air Nomad Emblem
Colours: Pale blue symbol, pale grey background
Civilization Ability - The Element of Freedom: Cities other than the capital generate 1 Faith per turn for every two tiles between them and the nearest Air Nomad city, (Doubled to 2 Faith per turn after researching Theology) and gain 1 Amenities and generate 1 Great Prophet point per turn for every five tiles between them and the nearest Air Nomad city. Cannot settle new cities within ten tiles of an existing Air Nomad city. Whenever an Air Nomad military land unit is targeted by a melee attack, there is a 1/3 chance it (and any units it is escorting) will instead move backwards one tile and take no damage.
Unique Unit - Flying Bison: Unique Air Nomad Support unit, unlocked by researching Horseback Riding. Has a movement speed of 5, pays only 1 movement point per tile regardless of terrain, can travel on to water tiles without embarking, and can travel through normally impassible terrain such as mountains or ice. Any non-cavalry non-naval units in formation with a Flying Bison also gain these traits. Does not upgrade into any unit, and never becomes obsolete.
Unique Infrastructure - Air Temple: Air Nomad unique District, replacing the Holy Site. Non-military units can be airlifted to and from tiles adjacent to an Air Temple, (Military units can be airlifted as well after researching the Rapid Deployment civic.) and cities with an Air Temple exert Loyalty pressure on all other cities with an Air Temple belonging to the same civilization, regardless of distance. Additionally, the Air Temple receives a major adjacency bonus from Mountains rather than a standard adjacency bonus, and costs half the production of an ordinary Holy Site to construct.
Leader - Gyatso (Vow of Non-Violence): Unimproved sources of crabs, deer, fish, furs, ivory, and whales provide +3 faith, but do not provide food, production, or gold, and cannot be improved or harvested. Horses and sheep each provide +2 faith, but no food, and cannot be harvested. (But can be improved.)
Leader Agenda - Peaceful Wanderer: Will seek to found cities much further away than other leaders, in accordance with the Air Nomad Unique Ability. Is also very reluctant to declare war. Likes civilizations that border him, have mutual Open Borders treaties with him, or send Trade Routes to his cities. Dislikes civilizations that declare many wars.
Cities:
- Southern Air Temple (Capital)
- Western Air Temple
- Northern Air Temple
- Eastern Air Temple
- Air Temple Island
- Patola
- Yangchen
- Laghima
Symbol: Water Tribe emblem
Colours:
- Light blue symbol, navy blue background (Sokka)
- Navy blue symbol, white background (Yue)
Unique Unit - Healer: Unique Water Tribe Support unit, unlocked by Apprenticeship. Units adjacent to a Healer heal 10 health per turn, increased to 20 health per turn if the Healer is adjacent to a lake, coast, or river. Upgrades to a Medic.
Unique Infrastructure - Igloo: Unique Water Tribe Improvement, unlocked with Masonry. Provides +1 food, +1 production, and +0.5 Housing. Food and Housing bonus is doubled if adjacent to either two (or more) Igloos or a City Center and one (or more) Igloo. Can only be built on Snow tiles.
Leader - Sokka (The Ideas Guy): Receive a free random Inspiration or Eureka (prioritizing earlier techs and civics over later ones) whenever you discover a new civilization or city-state using a naval unit. +1 Science from Fishing Boats and Igloos.
Leader Agenda - Clever Warrior: Likes civilizations with a technologically-advanced military, as long as they do not declare many wars. Dislikes civilizations with technologically-advanced militaries if they frequently declare war.
Leader - Yue (Moon Spirit): Population loss and unit damage from blizzards and floods is reduced by 75%. Population loss and unit damage from blizzards and floods is doubled for civilizations at war with the Water Tribe. The chance of a blizzard or flood occurring in Water Tribe territory is increased by 10% for every hostile military unit within Water Tribe territory. +2 Faith from Fishing Boats and Igloos.
Leader Agenda - Respect the Balance: Likes civilizations that have a high Faith output and respect the environment. Dislikes civilizations that have a low Faith output and disrespect the environment.
Cities:
- Agna Qel'a (Capital)
- Harbor City
- Foggy Swamp
- Chuje
- Kuruk
- Hakoda
- Kanna
- Arnook
Symbol: Earth Kingdom emblem
Colours:
- Green symbol, yellow background (Kuei)
- Silver symbol, dark green background (Kuvira)
Unique Unit - Disc-Thrower: Earth Kingdom unique ranged unit, replacing the Crossbowman. Has 55 melee strength when defending (equivalent to a Musketman.) and starts with the "Garrison" promotion, but has a range of 1.
Unique Infrastructure - Monorail: Earth Kingdom unique building which does not replace anything, is unlocked by Construction, and is constructed in the City Center. Culture generated by a city with a Monorail generates 10% more Domestic Tourism, increased to 30% more Domestic Tourism after researching Combustion, and units starting their turn in a city with a Monorail gain +2 Movement. Additionally provides 2 Housing.
Leader - Kuei (Grand Secretariat): Gain access to a unique governor: Long Feng, the Grand Secretariat. Long Feng's Titles are extremely powerful, but the city where he is established loses 4 Loyalty per turn instead of gaining 8 Loyalty per turn. Additionally gains access to the "Dai Li Agent" Unique Unit after researching Civil Service.
Leader Unique Governor - Long Feng:
- Title 1 - "No War in Ba Sing Se": (Default) The city where Long Feng is established does not suffer from War Weariness.
- Title 2 - "Here We Are Safe" (Requires No War in Ba Sing Se) The city where Long Feng is established is immune to all damage unless its Outer Defenses are at 0 hp. Outer Defenses in the city where Long Feng is established are not destroyed upon reaching 0 hp, and passively regenerate 25 hp per turn.
- Title 3 - "Here We Are Free" (Requires Here We Are Safe) Amenities and Housing are doubled in the city where Long Feng is established.
- Title 4- "Guardian of Traditions" (Requires No War in Ba Sing Se) If Long Feng is established in the capital, gain a free Wildcard Policy Slot.
- Title 5 - "Protector of Heritage" (Requires Guardian of Traditions) Culture (but not Tourism) from Great Works is tripled in the city where Long Feng is established.
- Title 6 - "The Grand Secretariat" (Requires Here We Are Free or Protector of Heritage) Foreign spies cannot perform missions in the city where Long Feng is established.
Leader Agenda - Harmony Restoration Movement: Likes civilizations that do not settle cities on continents other than their home continent. Dislikes civilizations from other continents who settle cities on his home continent, and hates civilizations from other continents who conquer cities on his home continent.
Leader - Kuvira (The Great Uniter): Killing a military unit on the Earth Kingdom's home continent causes foreign cities within nine tiles to lose 10 Loyalty, and Earth Kingdom cities within nine tiles to gain 10 Loyalty. Both of these bonuses are doubled if the defeated unit is a Barbarian. +1 Science and +1 Production from mines built on copper, mercury, silver, aluminum, or iron.
Leader Agenda - New Earth Empire: Likes civilizations with capitals on other continents who wage war on civilizations and city-states on the same continent as their capital. Dislikes civilizations with territory on her home continent, regardless of the location of their capital.
Cities:
- Ba Sing Se (Capital)
- Omashu
- Gaoling
- Zaofu
- Taku
- Kyoshi Island
- Qinchao
- Gaipan
