On either 2-2, 2-3 or 2-4 (Jungle or Volcana) , you will encounter a character in blue hooded robes standing in front of a wooden structure with a wooden moon sign above it.
The character will ask for 10,000 gold for you to participate in the Moon Challenge. Pay her and enter the door behind. You will be given a Mattock (pickaxe) and a four leaf clover (this extends the ghost timer by 2 minutes.) Once you pass through the laser trap, use
to dig through the lower area, you should find an assortment of gold, jewels and item crates as well as Hon Yi's Bow.
Once the Mattock is destroyed through usage, the challenge will be complete and you've got the achievement.