Throughout your journey, you'll collect various key items and artifacts that are crucial for story progression and unlocking the final areas of the game. These include the Energy Transfer Modules, which are required to reactivate the Great Temple's energy network, and the Sky Temple Keys, which are necessary to access the Sky Temple and confront the final boss. Each key is guarded by a powerful Ing-possessed creature or hidden behind a complex puzzle.
Other key items include the Dark Suit and Light Suit, which are not just defensive upgrades but also act as keys to certain areas or provide immunity to environmental hazards. The Screw Attack, while a mobility upgrade, also functions as a key to break specific blocks. Collecting all these items is mandatory for completing the main storyline and achieving 100% completion.