Can you explain main difference from mere aliens?
I thnk its something like this:
(Correct me if wrong)
Mere aliens are single entity. They are like a single human or the current single alien u see. Shoot it, kill it, it dies and stay dead. Stun it, its stunned and captured after battle.
Mounted aliens are more like single entity alien on a "vehicle" of sort. Think of it like calvaries (Soldiers on horses) or Battletech-styled (humans in Mech aka robotech?). "Kill it" (Destroy the robot) and perhaps the alien within has a chance of survival, pops out (hurt partially or completely unhurt) and now u have 2nd enemy to kill and take down.
Get the idea? Its simply a pain in the butt to code anything like this.....
BUT perhaps good can come out of this idea.
Winter - Is there a possibility whereby if humans have remote-controlled-tanks (UGVs), then aliens have similar single-entity-robots (thnk of it as droids / drones) which are tough to take down but possess superior research materials or the sortas? Or simply think of them as terror-machines? Just an idea.