AirMech Arena

This is as straightforward as it sounds, however it does take longer than you might expect if you're boosting this, and there are a few tips to take advantage of.

To get this done fastest, you'll want to find a boosting buddy and load up a custom match. Almost any map will work well, but try to pick a map that doesn't have much defenses near your bases so that you won't get shot down accidentally. Again, not much of an issue.

The biggest problem is the respawn time--20 seconds, unless you spend 2000 in-game credits to lower the timer by one second every other second, which only activates after 5 seconds of the respawn timer have passed. Short story, wait 5 seconds, start spending 2k credits and you can respawn in about 11-12 seconds.
You will want to equip the regular Kira pilot for the extra +30% faster respawn, and that should cut down respawn times down to about 6-8 seconds.
The other big problem though is that there is NO progress shown in the achievement tracker until the match finishes!! So keep very careful count.

You will also want to upgrade all the offensive capabilities of your AirMech(don't upgrade the armor!!) to help shoot down your partner faster, and the Warthog is recommended as it has the highest damage output. It uses energy extremely fast however so I also would recommend using the Energy Guardians to keep the Warthog's energy from disappearing too fast. Land and don't move in between attacks to regenerate some energy.

Last point--don't forget to move away from the base so that your AirMech isn't regenerated by your base! I made that mistake a few too many times.

It will take about 45 minutes or less for both players to get this once you get the hang of it. It really is quite easy, just feels like it takes a while.