There are several unused sprites in icons.png:

• A red-outlined and second white-outlined empty heart
• A red-outlined and second white-outlined empty hardcore heart
• A red-outlined and second white-outlined mount heart
• A red-outlined, brown-outlined, and two white-outlined empty food icons
• A pink boss bar
• A half and full blue armor icon outlines
• Lighter versions of the full and half food icons
• Lighter versions of the full and half hunger food icons
• A backward full food icon

If any of these icons are used, please tell me what they are. If they don't, why are they in the game?

People have reported these already, this is a compilation of the ones I've seen.