This achievement requires that you find a special artifact which can only be found by hitting a specific random Concealed Cavern event and then making some specific choices. You are looking for "the remains of Armageddon" which lets you choose between a sword, shield, or skull. Pick any of the 3 but DO NOT play them as they purge themselves. After a few levels you will get stopped right before the boss and given the flower artifact which changes the spell you chose to consume rather than purge.
Relying on a random event isn't why you came here, so we'll be using a seeded run that was posted by Schpeuch on Steam:
From the main menu, select:
- Community Challenges - Play
- In the Join Challenge section type in: BasementDepositTones
- Hit the right arrow button
You will find the event in the 3rd area no matter what route you take (its at the place where the tracks rejoin). If you happen to make a mistake you can retry as much as you need.