Key Items are unique, often story-critical items that cannot be sold or discarded. They unlock new areas, provide essential tools, or advance the plot:

- Pokédex: Records information on all Pokémon you've seen and caught.
- Town Map: Displays the Sinnoh region map.
- Running Shoes: Allows you to run by holding the B button.
- Bicycle: Allows for faster travel on land.
- Explorer Kit: Grants access to the Grand Underground.
- Fishing Rods (Old Rod, Good Rod, Super Rod): Used to fish for Water-type Pokémon.
- Coin Case: Stores Coins for the Veilstone Game Corner.
- Dowsing Machine: Pokétch app that helps find hidden items.
- SecretPotion: Cures the Psyduck on Route 210.
- Storage Key: Unlocks the Team Galactic Warehouse.
- Griseous Orb (Platinum only): Boosts Giratina's Ghost and Dragon moves.
Always check your Key Items pocket if you're stuck or looking for a specific tool to progress.