Key Stones are used along with a Pokémon with a Mega Stone in order to Mega Evolve. They are typically embedded in a personal accessory worn by the trainers.
Known trainers with a Key Stone
- Calem's Mega Ring (as the player or rival, uses on Absol)
- Serena's Mega Ring (as the player or rival, uses on Absol)
- Brendan's Mega Bracelet (as the player or rival)
- May's Mega Bracelet (as the player or rival)
- Wally's Mega Pendant (uses on Gallade)
- Korrina's Mega Glove (uses on Lucario)
- Lisia's Mega Tiara (uses on Altaria)
- Lysandre's Mega Ring (uses his specially invented cybernetic "Mega Ring" on Gyarados)
- Maxie's Mega Glasses (uses on Camerupt)
- Archie's Mega Anchor (uses on Sharpedo)
- Diantha's Mega Charm (uses on Gardevoir)
- Steven Stone's Mega Stickpin (uses on Metagross)
- Zinnia's Mega Anklet (uses on Salamence)
- Red (uses on Charizard - Mega Charizard X)*
- Alain's Mega Ring (uses on Charizard to become Mega Charizard X)*
- Remo's Mega Parasol (uses on Garchoo)*
- Astrid's Mega Earring (uses on Absol)*
- Siebold's Mega Buckle (uses on Blastoise)*
- Gurkinn's Mega Glove (uses on Lucario)*
- Mabel's Mega Staff (uses on Mawile)*
- Meyer's Mega Belt (uses on Blaziken)*
- A trainer's Mega Watch (uses on Venusaur)*
- A trainer's Mega Turban (uses on Alakazam)*
- A trainer's Mega Puppet (uses on Banette)*
- Malva's Mega Charm (uses on Houndoom)*
- Wulfric's Mega Locket (uses on Abamasnow)*
- Trevor's Mega Camera (uses on Charizard to become Mega Charizard Y)*
- Sawyer's Mega Bookmarker (uses on Sceptile)*
- Professor Sycamore (uses on Garchomp)*
- Chymia's Mega Bracelet (uses on Gardevoir)*
- Brock's Mega Charm (uses on Steelix)*
- Misty's Mega Hairband (uses on Gyarados)*
* - Anime only