how to create a "coop" mission?

[theOden]

"Let AI loose", mm not too detailed of me to be honest

Add an enemy flight.

Set them as "Script spawn"

Create a trigger named "workHarderLuthier"
Set it as "Pass through" for your AirSide and make it cover where you guys will be heading after take off.

Create an "Action" named "workHarderLuthier" to "Spawn Group" and click the enemy flight.

Important, they need to have the same name.

Mind you, this will trigger once for both of you so make the enemy flight "half size" maybe? - easier to control in C# code but I'm not sure how confident you are on that level.