If you are looking for a "piece" to complete a larger set, it's likely one of the three fragments of the Dancing Dragon Mask :

Sold by the Dungeon Memorial Mob near the Abandoned Dungeon Entrance for 5,000 Sen. 2. Key Prosthetic "Pieces" (Early Game)

If you're looking to increase your health ("properly" buffing your character), you need (found after mini-bosses) or Gourd Seeds (to increase your healing flask uses).

Since the "v1.02" tag is often associated with early release versions or specific community-repack discussions, here are the most likely "pieces" you might be looking for: 1. The Dancing Dragon Mask Pieces