The most efficient way I found to do this is with 3 controllers.
- Game Mode: Infiltration
- Player 1 on a team by itself
- Player 2 and 3 on a team together
- Map: Overclock
When you start, using player 1 go and find the beam weapon, the pickup icon is a kind of dark pink/orange. Then go and stand in the bottom left corner, just below the starting zone, and face right.
Then take controller 2, and drop out of the starting zone, and walk all the way left next to player 1, and jump up into the opposite starting zone.
Then take controller 3 and do the same thing. The mimic for player 2 will follow shortly afterwards, as the mimic reaches the centre of the zone, shoot using
on controller 1.
Continue into the opposite start zone, which will trigger the player 3 mimic to start. Take controller 2 and continue this pattern: Run across with a player, kill the mimic running behind using controller 1.
Here is a video showing the above: