Momodora: Reverie Under the Moonlight

The Imp Girl can be found very early on in Sacred Ordalia Grove. She is located just after and below the second save bell, and just before the boss.

The Dirty Shroom is located in the Subterranean Grave, in a narrow passage near a save bell underwater. You will need to get an item to fit into the narrow passage:

You can use a shortcut between the Whiteleaf Memorial Park and the Subterranean Grave to backtrack to where the Dirty Shroom is.

Once you have attained the Dirty Shroom, backtrack to Sacred Ordalia Grove to give it to the Imp Girl and:

Achievement unlocked!

Thanks to the following references:

Hope this helps and saves some time researching!

Welcome

Here is a video guide shows the process for this achievement.

The only thing you need to attempt this is unlocking the cat sphere form which comes from normal progressing through the game.

Credits goes to Rikku Kirru channel