Three Car Garage (10 player)

If you want to solo this, a demolisher is really the only vehicle that can solo kill the boss. So if you wan to solo this, you need to bring the other vehicle you want credit for into the arena. Then get into a demolisher and park near the other vehicle. I use a rotation of pyrite-blaze-blaze. The pyrite puts a DOT on the boss. When it gets to about 5-10%, hop out of your demolisher and hop into the other vehicle. The DoT should bring him down, and bingo.

Really easy to do after 6.0.2. Was missing the siege engine part. I parked my siege engine close by (same should work for chopper). When he came out, I jumped out of the vehicle and kited him down to around 10% (was still at 100%), then jumped back into my siege engine and finished him off for the achieve. Any ability that gives you speed boost should help too.

According to the notes for patch 7.3.5 (January 15, 2018), this achievement has been replaced by this one. The new achievement does not distinguish whether the raid is 10 or 25 player.