Robotnik once has a scheme to replace the official Mobius mint with currency featuring his image. Sonic naturally stops this plan, but in a later episode he has King Komomats imprison Sonic to "protect the planet". Sonic speculates that Robotnik probably paid the King in counterfeit money, and when he checks said money, it has Robotnik's face on it. Since Sonic stopped Robotnik before his currency could be made official, it is indeed counterfeit.
There's a Running Gag in "Sonic is Running" wherein Robotnik's robo-dog created for his campaign keeps attacking him. In addition to the Visual Pun of attacking Robotnik's heel (as well as being a heel), the dog was mentioned to have been made with a heart of gold. So, of course it would refuse to obey an evil man like him.
It's perhaps even more horrific that Sonic does nothing to restore Blackbeard to humanity despite his status as a victim of Robotnik's scheming. Last we see, he's reduced to nothing more than a pile of scrap metal doomed to forever drift down the ocean... although I guess you could argue that he had it coming simply by virtue of being a dirty rotten thievingPirate.
There's the underlying implication that despite his bumbling tendencies, Robotnik would probably have taken over Mobius and harmed far more people if Sonic and Tails weren't around to stop him. "Mass Transit Trouble" provides a good example of what could potentially happen.
Just what exactly did Momma Robotnik do to him growing up that made him so evil, aside from trying to make him into a Card-Carrying Villain? And do we really want to know?
In "Hedgehog of the Hound Table", it was explained that holding the Chaos Emerald of Invincibility alone wouldn't activate its power—to use it one must be crowned king, as Robotnik discovered earlier. But when Tails holds the Emerald he uses its powers with no problems at all, despite not being the king.