Must be done solo (Instant Action) - Can be glitchy
You can play however you feel comfortable with, as long as combat mode is set to "One Man Army" and you have to win the game or course. From the main menu, choose Instant Action. Easiest settings are the same as usual:
Map: pick any you like
Mode: MUST be "One Man Army"
In regards to the glitchy part, I used above settings on the Nuclear Dawn map, won the game but the achievement didn't unlock.
Used the same settings over again but this time on the Edge of Oasis map, and got the achievement.