You could place NPC's and edit their factors:
Enemy?- If they shoot at you
Set path
Advanced pathing (setting up rolling maneuvers)
Squad?- if they loosely follow you and shoot at enemies
You could also have different objectives
-Capture point- This would be for ground missions only, where you would have to capture a set point and bleed out the other team, like Battlefield 1942
-Linear objective- You set a checkpoint for the vehicle to reach, and when that checkpoint is reached, it either ends the mission, or places another checkpoint (can also be timed)
-Bomb run- You must bomb and destroy either a convoy or a destructible town, base, etc.