This achievement is a lot easier than it looks. All you need to do is beat a players score within your Choas Squad game. To know if someone has it, look if they have a skull with two swords crossing to make an x by their name on the lobby leaderboard.
It'll be easier if you have fully leveled up weapons and are somewhat familiar to how chaos squad works. The oil rig only has 3 missions before the night defense. It's also worth noting that this can be achieved regardless if you beat the night defense or not.
Edit: As a lot of people have been claiming, this achievement will pop if you have the dlc or not, if the requirements are met. So if you don't feel like buying the dlc or wanted to wait for whatever reason, be careful when playing chaos mode.