Tainted Grail: Conquest

There is a special encounter/location that you can find called the hunting grounds (I think). You can either try to rest or hunt for food. If you choose hunt for food, you will face some easy to beat animals. When you win the fight, you should get 10 pieces of meat. Each meat will heal 5 HP.

Make sure the meat is in your item hot bar so that you can use it in combat. Then if you are missing at least 50 health in a fight, just use all 10 of the meat and the achievement should pop.

The another guide is great if you can find the hunting ground during your runs toward completion but if it doesn't spawn even once during your multiple runs due to the RNG nature like my situation, you can easily unlock this one by starting a new save, skip the fight by ending your turns (holding each turn)until you die, once you move out of the village you will be given some wyldcandles, your inventory at this moment is 8 candles and 2 potions, open up inventory by while holding , move the candles from upper grids to below combat item slots by and , then make your way to the closest enemy and use up all 10 of them by or then , achievement pops