Play a 1 vs 1 with a friend and get him to buy no units, then use a leader power on his scout unit.
The achievement can also be earned on the campaign level "Scarab" by killing the scarab with a MAC blast.
- The name is a reference to a "walk-off home run" in baseball, in which a batter hits a home run in the bottom of the ninth inning or later, and in doing so adds enough runs to their score to win the game. As a result, both teams "walk off" the field once the winning run is scored.
- Even though the title says an "Enemy's last unit" you can actually get it by killing an ally's last unit with Regret's cleansing beam.