This achievement is for getting at least a 250 killstreak in Arcade Remix.
This can be done very easily if you unlock Schoolgirl Annie. Annie can be bought using acquired Zenny, I think I got her after about 4 matches maybe you can get her in less.
Annie has a very cheap heavy combo that propels you forward with a Spin Move on the last attack making it easier to chain the streak.
The easiest location to get this is in the first level in Ingleton when you are in the graveyard, there are zombies everywhere so it’s easier.
I did this in the video below and got over a 400 killstreak on the second killstreak
Also this is easier to do in a solo game.
UPDATE: Just found out you can just pull
to do Annie's Spin Move without doing the combo, so you can do that if you want!
Good Luck!