Somehow, the best co-op partner for me to get the ‘destroy 200 items from the gunner seat in co-op’ achievement, was a random 8 year old who just wanted to blow stuff up.
Everyone else I played with was either too egotistical, too unfocused, or just too plain stupid to be able to work with me. Not this kid. As soon as I jump into the co-op game, he’s like “hey there, I just want to blow stuff up.”
And I’m like, hells yeah.
(The best way to get it, of course, is to have a friend drive one of the badass vehicles while you fire away at targets, and call in replacement vehicles as necessary, then switch who drives and who shoots. But none of my Xbox friends actually have Mercenaries.)