Easily done in Team Destroy. Choose the level with the fountain, each team gets a turn playing as the Night Walkers for 20 min. If boosting with a friend simply run down stairs and kill opponent 20 times. Since they always spawn downstairs you can easily net 3 kills in 1 min (game is forgiving and can be done just outside of a minute) just make sure your buddy communicates where he spawns to make sure. Once your sure you have at least 20 kills simply destroy the objective and on their turn they quickly run down and destroy the objective as well (this will also unlock Destroyer for player 2 as well). At no point should the player not going for the achievements get a kill!!!! Start a new match and return the favor for your buddy.
Using this method will net you after 1 match:
350G from 1 match, enjoy the easy gamerscore
Co-credit to neudog