You will need to in control of Lily when you're in Clonfira.
As you make your way through the swamp, and need to reach the final section.
1: Approach the edge of the platform you're on, and a monster will grab you with its tentacle.
2: Quickly select your wooden sword from your inventory, and use it on the tentacle, but not the monster itself. That will waste valuable time.
You're achievement will now unlock should you have been quick enough.