1 Card and 2 Artifacts will guarantee this achievement for you.
Build
Pretty simple. Cleo has 40 Hull and 10 Shield. His cannon attacks deal a total of 42 damage on the first turn. Bring Peri and Max, and focus on getting a Parry card.
Your two artifacts to find are Piercer and Lightspeed Boot Disk. Apply the Buoyant effect from the Boot Disk artifact onto Parry.
Going into the Cleo fight, you will top-deck Parry, and one-shot Cleo with a piercing Parry. Max’s Lightspeed Boot Disk isn’t completely necessary if you have good card draw or can survive a turn or two to draw Parry naturally, but having all of these will guarantee a kill.
Note that I haven’t actually managed to do this yet, but it should work in theory assuming there isn’t a specific countermeasure for it
