Witch Train to Robotropolis is a short Sonic the Hedgehog story. It is based in the Adventures of Sonic the Hedgehog universe and was initially a collab with writers who wrote for The New Adventures of Sonic the Hedgehog.
After defeating Hei Hou, Sonic, Tails and Knuckles are about to head back, when Sonic suddenly collapses. After his friends express their concern, the hedgehog pulls back his glove cuff and reveals a watch, which says it's lunch time. Not knowing where they'll find something to eat, Sonic picks up the smell of chili and starts floating towards it. The other two follow him to a small, cutesy house, where the aroma was coming from. When they approach the front door, a small girl in a cute witch outfit answers and says they're just in time to join her for lunch. The three enter, but Tails has his suspicions about the girl, who introduces herself as Magnolia, and her house. Magnolia brings Sonic a chili dog, which causes his eyes to dilate. Knuckles then says he gets "that same stupid look" when he sees something, but doesn't get to finish his sentence as Magnolia brings some yogurt covered snacks and says they're black ants. Tails sees a few things in Magnolia's house that indicates she might be a sinister witch with wicked intentions. Before he can tell his friends about it and stop them from eating their meals, which they've already finished, they turn into a real hedgehog and echidna respectively. Magnolia cackles evilly and reveals herself to be a stereotypical wicked witch with green skin and warts. Tails grabs the transformed Sonic and Knuckles and flees the house as Magnolia tries to cast spells on him with her wand.
Tails then runs into Amy, and explains everything. Amy is devastated to see Sonic in his new state, and offers to help Tails confront the witch and turn them back to normal. They also learn Robotnik is setting up another train to deliver his weapons to another city, so they have another threat to stop. After finding an active bomb on that train, and found at a tight end, as they are cornered by Robotnik's badniks, Amy, in desperation, eats the bomb. The smoke that comes from her mouth acts as a smokescreen and they climb into the roof, where they see Magnolia flying over it. When Tails confronts her, she tries attacking them, which leads to she and Amy getting into a hammer/wand fight. Before Magnolia tries to cast a spell on Amy, at that moment, Amy pulls out a mirror from her pocket and reflects the magic blast towards the witch. Magnolia seemingly shrunk, but then hops out of her hat as a frog. Amy and Tails happen to find a spell scroll and the things needed, to undo the spell on their friends. When they successfully reverse the spell, Amy mentions how she enjoyed getting to hold Sonic as a real hedgehog, which makes him uncomfortable and mutter to himself to change back.