As is previously mentioned by the other two guides; outside of Joule's Crawler in the Granite Steps are two sets of level 2-3 spider-bots. These enemies are perfect for this achievement and the Split Focus achievement.
Damage the enemies using the RT gunfire mode, while making sure your corebot isn't attacking them by continually spamming the X button to call them to your side.
Once they are weak enough, it'll take some luck and timing to get them lined up. Below is my Game DVR footage of when I got Chrom-tastic! (It's cringey but I hope it helps)! :)