Slay The Spire

Start new game until you get to chose "enemies in your next 3 battles have 1 hp" and then you can just plan how to get to 1 hp and then kill the enemy. I got it on my first try, I was against 2 slimes (green hits 3 and steel hits 8) and when I had 31 hp left I killed the steel one and just use skip until I had 1 hp and killed the green one.

This is difficult to plan for and will likely just come naturally as you play through the game.

If you want to try to coordinate it, then you'll have to be mindful of enemy attack damage and attempt to balance it with blocks in order to get your HP to exactly 1. Once you finish a battle with 1 HP, this achievement will unlock.