Creating a map for this alternate game mode is simple. You can follow the same steps for a custom Mission map, as we've seen, with the exception that this time you don't need a Player Spawner. Also, you need to set the Map Type, in the LevelContainer prefab, to Ai Battle.
The last thing that you need to make sure your map has, is spawners with different factions, so that there are NPCs that can fight each other.
I'm making available here the Map Editor project I used to make the AI Battle 02 map, that you can see included in the game. Feel free to study this example to see the intended way to use Triggers and Receivers. In this case, I'm using those to make each NpcSpawner spawn a new NPC when the one spawned before dies, but only for 3 times. So, 3 NPCs per spawner.