Keep playing until you enter the Dungeon. This is all RNG, but there are three different prompts to unlock this achievement which requires you to obtain a magic mace.
1. If you get the prompt for Lever, do this:
2. If you get the prompt for Doors, do this:
3. If you get the prompt for Hole, do this:
Getting the magic mace can also earn you the Vanquished achievement later on, please see that for more information.