Beat the game.
You must:
- Collect all Heart Pieces and Heart Containers
- Active all Goddess Cubes and open their chests
- Collect all Gratitude Crystals
- Collect all Medals
- Collect all Bottles
- Collect all Pouch/Wallet upgrades
- Collect all B-items, fully upgraded
- Obtain all dowsing options
- Obtain the Hylian Shield
To clarify, the following are not required:
- Shield, ammo, or potion upgrades
- Dungeon maps
- Non-goddess chests
- Bird statues