Ring of Pain

I got this whilst stacking a few items that lower max health. I gambled on a curse potion and went from my max 7hp down to 1.
If you get on a run where you have a low max health value, look out for curse potions to try lower your health to 1. Curse potions will never kill you, instead leaving you on 1 hp, so they are a convenient way to lose the exact amount needed for this achievement

If you happen to find a fountain of life you can click on it until you have one health left, wich will unlock the achievement.