Again, easiest with a friend. Have one player create 77 Locusts while the other creates several Stalkers. Use the Stalkers' SAM ability to take out the Locusts. Make sure that the Locusts are just out of range of the Stalkers' normal weapons. The SAMs have longer range that their default weapons. Can also be done in campaign, mission 9. After you destroy 3-4 towers, 3 dragons will show up. If you build 6 Stalkers first and put them under their flight path, this again can be saved and then reloaded for a reasonably fast achievement. You aren't going to want those guys flying around anyway as you progress in the mission.