Select Battle from the Main Menu
You will need at least 2 controllers, a guest account will suffice.
Select "Classic Battle" Game-Mode, and then "Free For All".
Select Random Map.
to select character and costume (if unlocked) and navigate both characters to the starting pad.
Once the map loads, press
on both controllers.
Then you can quit the match immediately with
, "Back to Menu".
Repeat this 30 times for your achievement.
It took me about 15-20 seconds including loading (Xbox One X) per match, so 7.5-10 min for this achievement.