Beyond item upgrades, Link's core stats can be improved through Heart Pieces and the Stamina Scroll. Collecting four Pieces of Heart grants Link an additional Heart Container, permanently increasing his maximum health. This is crucial for survivability, especially in later dungeons and against tougher bosses. Prioritize finding these hidden collectibles as they become available.
The Stamina Scroll is a unique upgrade that increases the size of Link's stamina gauge, allowing him to remain merged into walls for longer periods. This is an invaluable upgrade for solving complex merge puzzles and traversing large wall sections without running out of energy. The Stamina Scroll is typically found in a specific location in Lorule, often requiring a bit of exploration to uncover. Maximizing both your health and stamina will make Link a much more resilient and versatile adventurer, capable of tackling any challenge the game throws at him.