The Dragonstone is another Magical Artifact which holds all of Dragon Magic inside. It was sought after by Opaline Arcana for her plot to regain her power in Missing the Mark but later it was returned to the Dragon Lands by Spike after Opaline's defeat in Roots of All Evil Pt. 2.
History[]
According to Discord, one day, a mysterious wicked unicorn pony (later to be revealed as Opaline Arcana in The Isle of Scaly) came along and caused pandemonium by convincing some ponies into hating each other. Soon all ponykind found themselves divided, which caused a terrible event to happen.
To make sure magic never pitted unicorns, pegasi, and earth ponies against one another, Twilight Sparkle gathered all the world's Pony magic and placed it in the Unity Crystals while placing all of Dragon Magic inside of the Dragonstone. As long as these crystals were protected, and all ponykind lived in harmony, magic would be kept alive and well in Equestria. In Chapter 4, it is revealed the Dragonstone was dormant in power until Opaline retrieved it.
In Chapter 4, "Missing the Mark" Opaline used the Dragonstone to nearly drain Sparky of his Dragonfire Magic and empowered herself with it.
In Chapter 6, "The Isle of Scaly" after capturing Lava and Jade, Opaline mind controlled them and forced them to use their Dragonfire on the stone, turning them into her servants.
In Roots of All Evil Pt. 2, Sparky used the Dragonstone to take back his stolen magic, draining Opaline's dragonfire power and returning the Mane Six's Cutie Marks and then used it to free Lava and Jade and cast his own spell on Opaline's Together Tree freeing all the other cutie marks in Equestria she stole and causing her to lose her own cutie mark and power and was sealed inside of the Together Tree, ending her threat to Equestria forever. Spike teleported the Dragonstone back to the Dragon Lands where it would remain safe.