From the world of Sonic The Hedgehog x My Little Pony

After defeating Eggman and restoring magic to Equestria, mysterious cracks open in the ground, releasing a dangerous gloom. Sonic the Hedgehog and Sunny Starscout then decide to investigate beneath the ruins of Canterlot Castle, unaware of the great danger they're about to face.

Alternate timeline created at some point after Sonic x Make Your Mark: Season 2

Inspired in The Legend of Zelda: Tears of the Kingdom and taking place in the world of Sonic The Hedgehog x My Little Pony: A New Generation, created by BronySonicFan.

Keep in mind, this story is not canon to whatever he's making so far. I just got his "blessing" to create this story and inspire it in his world.

Also, the Cover was made by him, so thanks for that!