The Adventures of Sonic the Hedgehog

So Robotnik and his robots head for the time of King Arthur and the Knights of the Hound Table. Robotnik meets Merlence the Wizard (and Scratch and Grounder get to fool around with a magic wand), who just hands him the Emerald of Invincibility. But holding the Emerald is just half the thing – you need to be king for it to work. So Robotnik takes over the throne and makes Merlence change Sonic's boots to stone. Sonic and Tails rescue Merlence and humiliate Robotnik so hard he loses the Emerald, then they send the Badniks to a Roman coliseum, and Sonic gets a knighthood.