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.
Robotnik mentions a mutual hatred of canines. One of his arch nemeses is a fox.
Why is the Sonic Sez topic for "Hero of the Year" alcohol? Scratch and Grounder were drowning their sorrows after failing to thwart Sonic's party.
"Grounder the Genius" demonstrates this even further. Grounder, given super-intelligence by way of a genius chip, usurps and even imprisons Robotnik and takes over his fortress and operations.
One for the Fridge Logic down below, after just watching "Hedgehog of the Hound Table". Apparently, all it takes to BE king just needs the crown. It doesn't have to be legally obtained. So with NOBODY wearing the crown... you get the idea. If not, anyone could use the invincibility emerald, as no one had the crown, hence, everyone was technically "crowned king".
This also explains why Robotnik could use the power of the emerald in "Prehistoric Sonic" even though he didn't take King Arfur's crown a second time, because in the future? Arfur is dead! There is no crowned king of Mobius.
Certain notes in Robotnik's leitmotif (most notably, the first note in most versions) have a few grace notes (notes which are played very quickly before the main note), giving them a trilled sound that mimics Robotnik's Trrrilling Rrrs.
Robotnik has a raygun that's basically a handheld version of SatAM's Roboticizer. In the Chaos Emerald saga, he even uses it to roboticize Blackbeard and several dinosaurs. If it wasn't for the Genre Blindness and Misapplied Phlebotinum, Adventures of Sonic the Hedgehog's Robotnik could easily be even more dangerous than SatAM's Robotnik.
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...
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.
Through the course of the series, the body count would probably be in the thousands if not for the intervention of Sonic and Tails. One of his earliest schemes in the series ("Lovesick Sonic") involves destroying a town and killing all of its inhabitants by flooding it.
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?
