Very easy way of getting this! Grab a couple friends, minimum of 3 (including yourself). Go in to an Arena match and select friends only.
Then once you are on the lobby screen, the two/three of you wanting the achievement go on the same team, and the other guy goes on a separate team.
Once the match starts, quickly beat him, then once you go back to the team selection screen, have the guy who just lost back out. This will leave you and your friend/s on the same team with no other people in the lobby. You then want to all ready up and you will receive an Insta win
once the game loads.
Once you're brought back to the lobby, just repeat the process and you'll get the achievement in 10-15 minutes, hope this helps! :)
I found this out playing with "M Hunter Nilin".Note:
It may be worth pointing out, to ensure the wins count, once all your friends are in the lobby, press
and change it to public and all of you ready up straight away, before someone has a chance to join. It's not necessary but I would recommend it, just in-case.MathGuy42
also pointed this out, for those of you using a second controller as the player who leaves. "
I had a second controller logged in with a different GT. The 3 of us were on one team against the second controller. I couldn't back out via the menu without taking both GTs out. However, by signing out the second GT in the Dashboard, the 3 of us were left in the lobby where game type is chosen. We just kept hitting
to vote for melee, then won instantly."