Go to village, then deathmatch and set up an offline 1v1 game with a 20 kill limit (incase you make mistakes). 1 controller have your main, achievement winning profile, and the 2nd a guest or backup profile.
Go to the bottom level with both characters. Have your main profile go to the VERY bottom left (so if you moved further left you'd screen wrap) and have your 2nd profile go to the VERy bottom right (so if you moved further right you'd screen wrap.
Then, press Left D button and
with the Main profile, and Right D button and
with the backup profile so they screen wrap into eachother and collide. If you configure tracker, you'll see the achievement progress rise by 10%. If you are struggling doing the timing on your own, get a friend / sibling / SO to help you out, but its really very easy. Repeat 9 more times and it'll unlock.