To unlock the Untouchable AR challenge, I have to "perform 3 Critical shots in one drone tank battle". What is a critical shot and how do I make one?
Use the vulcan (machine gun) to hit them right in the sensors. There's a cutscene where you discover that fact. You get a critical by blowing them up by hitting that spot (it'll show as a yellow critical thing on the left side above the combo meter).
You can also get a perfect hit by hitting that spot on the first shot. All using the vulcan of course.
The sensors are the blue lights on the right side of the smallest drones for example.