Letter Quest: Grimm's Journey Remastered

This is one of the more difficult achievements to obtain, only because it's very difficult plan it out ahead of time. It's possible you will get lucky randomly at some point while playing, but most likely you'll get through the game without ever being damaged down to 1 health remaining.

If you want to try to plan it out ahead, enemies do a set amount of damage (unless they critical hit), so you could try to calculate how much damage they do and subtract it from your total health to see if they'll leave you with 1 health.

If, like me, you make it to the end of story mode and haven't gotten this achievement but you've gotten all the upgrades, a guaranteed (albeit very long and boring) way to get this achievement is to go back to stage 1 and let the enemy attack you. Assuming you have all of the defense upgrades, he will only do 1 damage when he hits you. Press to swap tiles (which essentially skips your turn) and just allow the enemy to continually attack you until you're down to 1 health, then kill him to finish the stage.

IMPORTANT: Make sure you don't have anything equipped (books or weapon) that will give you health or convert damage to health so you don't spend all that time getting to 1 health only to regain some health when you kill the enemy! ALSO NOTE that orange crystals regain health, so avoid them when going for this achievement!