This could be gotten with in the first hour or two of the game. Can be done on
ANY difficulty, including
Just the Story! (Recommended) Video guides for the quests at the bottom.
First when you get into town and leave the pub go over to the Notice Board and take the Contract:
Devil by the Well follow the quest up to the battle. Fight the Noonwraith with
ONLY your Silver Sword,
DO NOT use an Oil, Potion, Sign, Bomb or Mutagen.
That's 1 down, second is going to be The Griffin in the main quest
Beast of the White Orchard . You pick this quest up by following the Main quest
Lilac and Gooseberries. Again follow the quest to the part where you meet Vessemir in the field and get the crossbow.
I DID NOT USE THE CROSSBOW, I don't think that changes anything but just in case, don't use it. The battle is easy enough. Use
ONLY your Silver Sword.
The achievement pops right after you defeat the Griffin.
Edit: You CAN drink water and eat food to heal during the fight
Edit 2: I took out the walkthroughs and added my own person fight recordings to the guide. I started a new save just to record these and from the first cutscene I finished both quests in around 35 minutes. Very easy with starting gear!
Edit 3: Sharpening your weapons WILL NOT void the achievement
Devil in the Well Fight:
The Beast of the White Orchard: