Key Items are unique, story-related items that cannot be sold or discarded. Examples include the Mega Ring, Bicycle, Dowsing Machine, and various Badges. They are essential for progression or unlocking new features. Collectibles include items like Fossils (which can be revived), Evolution Stones (Fire Stone, Water Stone, etc.), and various Berries (which can be grown and used in battle or for Pokémon-Amie). Finding all collectibles adds to the completionist experience.
