Hearts, Gratitude Crystals and sky rewards
Complete Skyloft's character errands and search for loose Gratitude Crystals at night. Return to Batreaux at each reward threshold.
A struck Goddess Cube unlocks a chest elsewhere in the sky. Track the cube and the chest as two steps so an activated cube is not mistaken for a collected reward.
Revisit surface regions with swimming, Clawshots and improved digging. Finish bottles, heart pieces and equipment upgrades before optional endurance challenges.