In Pokémon Diamond, Pearl, Brilliant Diamond, and Shining Pearl, Buck takes the Magma Stone from Stark Mountain, but returns it after receiving advice from his grandfather at the Survival Area. In Pokémon Platinum, Charon takes the Magma Stone from Stark Mountain, but Looker has his Croagunk confiscate it; after Charon is arrested, Buck takes the Magma Stone back to its resting place. Once the Magma Stone has been returned, the player can encounter a wild Heatran where the Magma Stone originally rested.
The Magma Stone appeared in The Magma Stone. It was removed from its stone altar inside Stark Mountain by Charon, causing Heatran to awaken and go on a rampage inside the mountain. With the help of Looker and his Croagunk, Buck ultimately managed to return the Magma Stone to the altar, resealing Heatran and making it disappear.
The Magma Stone first appeared in Interrupting Ivysaur. Buck decided to protect it from Team Galactic by taking it away. However, in Exit Empoleon, it turned out that upon removing the Magma Stone from its spot, he had unwittingly unsealed Heatran, allowing Charon to capture the Lava Dome Pokémon.
Pokémon Diamond and Pearl Adventure!
The Magma Stone appeared in A Clash! Hareta vs. Charon and The Anger of Legendary Pokémon Heatran, where it was knocked off of its pedestal due to Charon's activities at Stark Mountain, causing Heatran to go on a rampage. The stone was eventually restored to its rightful place by Hareta, calming Heatran down.