Hey guys, a video tutorial is on the way but before it uploads I will give a very in depth explanation of how its done!
Before you get started, it is absolutely necessary to download IGE, or In Game Editor, which you can find in the steam workshop. If you do not want to input anything in the game once its started, you will also have to disable the World Congress. To do this, navigate to
C:\Program Files (x86)\Steam\steamapps\common\Sid Meier's Civilization V\Assets\DLC\Expansion2\Gameplay\XML\GameInfo\CIV5 GameOptions_Expansion.xml
Open CIV5GameOptions_Expansion.xml with Notepad or Notepad++ and you'll see:
<Type>GAMEOPTION_NO_LEAGUES</Type>
<Description>TXT_KEY_GAME_OPTION_NO_LEAGUES</Description>
<Help>TXT_KEY_GAME_OPTION_NO_LEAGUES_HELP</Help>
<Visible>0</Visible>
Change <Visible>0</Visible> to <Visible>1</Visible>
Now when you go to Advanced Setup you'll see an option to "Disable World Congress", this is important later.
After this is done, you must start the game after downloading the mod and select "mods" from the start menu. Next, ensure that IGE and any other mods (like custom civs) you want to use are enabled.
Now you can setup a game like usual, choosing your map type, civs, gamemode et cetera. I usually only enable domination victory for my videos, as this makes for a more interesting AI game. Disable the world congress using the new option you enabled earlier, it will be in the advanced setup screen of your game.
Once you start the game, however, you need to ensure several steps are taken to make the game AI only. First, click the IGE button on the top right of your screen. If you don't see this, you have to make sure the mod downloaded and is enabled correctly. Assuming it is, click on IGE and then click on the PLAYER tab. Your civ will by default be selected, so use the menu on the left to select "reveal map / reveal all", this will disable cloud of war and allow you to see all the moves of your AI nations once the game begins.
Next up you will want to select the unit tab in IGE. Once this tab is selected, scroll to the right, and select either a submarine or a nuclear submarine. Once this is selected, right click on the far corner of your game map, near the clouds on a small map or under an ice sheet / iceberg on a normal map to spawn the hidden unit. Next, click the tile editor tab and scroll to the far right. You will see a button called "your land", click it and right click where you spawned your unit. This is to ensure that no other civ will spread their culture to your hidden submarine, which can and will end your game if a civ spreads a tile there.
After you have placed your submarine (with your one tile ownership in place), select the city / tile editor. Now click on your settler and warrior that you started the game with, and delete them using IGE. The delete command can be found in this menu. Once deleted, you are ready to start your game.
Ensure in the in game options that single player auto end turn is checked and enabled. Now, select your submarine and press " f" to sleep the unit.
Now everything is completed and you are ready to witness your AI civs battle each other ! I hope this helps, let me know if you need any further help and have fun!