Paper-Thin Disguise: Much of Sonic's disguises are this. One's just Sonic with a hat and a bag of mail, and they fall for it.
Lampshaded by Sonic when, to his alarm, sufficient doses of downloaded ninjutsu allow Scratch and Grounder to see through a disguise.
Also in the episode Grounder the Genius twice. The first time Sonic visits the fortress as a "Chip Recycler" and looks for the genius chip. Grounder says he has it which Sonic tries to get him, however Grounder, now being a genius, petrifies him aware that this would happen. Another example is later where Grounder makes out a trap and tosses it away far before anything bad happens. Sonic takes off his disguise and Grounder states he already knew Sonic was going to pull that.
In "Too Tall Tails" Sonic actually takes off his disguise mid way through one of his schemes. Scratch and Grounder still don't recognize him!
Dr. Robotnik actually does manage to see through the majority of Sonic's disguises, however the few times he does it is either a few moments too late, or he's too far away to tell Grounder and Scratch, the ones typically being tricked.
Parental Substitute: To Tails, who happily accepts that Sonic's his "mom, dad, and picket-fence".
Only Known by Their Nickname: You can count the times he's called "Miles" on one hand. This actually becomes a plot point in "Tails' New Home", when a couple appears claiming to be his parents. Sonic eventually realizes that, if they were really his parents, they shouldn't have been calling him Tails; they should have been calling him Miles.
Beware the Silly Ones: It is often implied Robotnik is only ineffective due to Sonic. A lot of episodes show the heroes encountering civilians that have already been enslaved or terrorized by Robotnik due to Sonic not being around. Not to mention the odd occasion Robotnik even manages to get one over the hedgehog.
Big Beautiful Man: In his own mind, at least; the chief animator paid special attention to trying to convey this, in hopes of making Robotnik "animation's sexiest fat man". Of course, the reality is that, in-universe and out, Robotnik's "sexy moments" are serious Fan Disservice.
Butt Monkey: Sonic pulls no punches making him suffer. One of the best examples is the "Zoobotnik" episode.
Card-Carrying Villain: Played with. Sure, he likes being called despicable but there are moments when he will pretend to be a hero if his plans require it. An example of this would be Over The Hill Hero, where he says to Captain Rescue "I think we can fight rotten-ness just as good as that hedgehog..
Even Evil Has Standards: Loathes his cousin, Dr. Warpnik, for being a creepy, freaky, utter loony with an unsettling fixation on fish. To the point he sealed him up in a pocket dimension called the Warp of Confusion to get him out of everyone's hair.
Freudian Excuse: Dr. Robotnik is implied to have one in the form of his abusive mother, Momma Robotnik.
Gadgeteer Genius: As buffoonish as he is, most of his gadgets do what they are supposed to and are pretty damn advanced.
Genre Savvy: He may not fare much better than Grounder and Scratch in the department of victory, but at least he knows enough to try different methods to keep Sonic away (such as tempered steel and tricking people around Sonic rather than getting Sonic himself), and even then always assumes Sonic will show up and take out Scratch and Grounder at the minimum.
My Beloved Smother: Robotnik, despite his evil nature, is completely at the mercy of his mother, who is even more demanding and has a really bad temper. He has turned on her a couple of occasions though.
Not-So-Harmless Villain: Usually rather bumbling and defeated handily by Sonic. There are a fair few times he manages to outsmart the hedgehog and temporarily get the upper hand however. It helps he also knows just how to get under Sonic's skin (see above).
Pet the Dog: In the first Mama Robotnik episode, he shows he sincerely loves and cares for his "Fuzzy-wuzzy", the teddybear he grew up with a child and which was his only friend. True, Fuzzy-wuzzy is a killer robot that basically turns into a creepily real grizzly with four arms and two heads, but he still loves him all the same, even begging Sonic to save Fuzzy-wuzzy from being destroyed and promising to stop his latest evil plot.
Robotnik's newest, dedicated anti-Sonic robots and general minions. Unfortunately for him, they're both total incompetents and idiots. Created at about the same time from the same machine, they would originally have been identical, but Scratch pulled a lever that caused Grounder to come out with a different chassis. Both Badniks are based off of badniks from Sonic the Hedgehog 2; Grounder is a straight lift of the Grounder badnik (itself a lift of Burrobot from the first game), while Scratch is a heavily modified Clucker (a turret-firing chicken badnik).
Affably Evil: In "Grounder The Genius" when Grounder gains super-intelligence, he also gains a considerable amount of charm to his personality.
Evil Laugh: Scratch's rooster laugh, which sounds like a trumpet.
Genre Blindness: Sonic tricks Grounder and Scratch endlessly all the time with various disguises, yet as far as they seem to know there's just a lot of hedgehogs all over the planet with a series of different and very diverse jobs.
Genre Savvy: Scratch has his moments, occasionally being able to see through Sonic's disguises and tricks sooner than Grounder. Though it's often too late to do any good, or it turns out to be a trick within a trick.
Harmless Villain: While Robotnik could at least strive to be fearsome every now and then, Scratch and Grounder were completely incompetent for the large majority of the time, when not being defeated easily by Sonic, their plans were taken apart by random civilians or even their own bumbling.
One of Robotnik's earlier creations; pushed aside in favor of Scratch and Grounder, Coconuts yearns to re-earn Robotnik's attention and affection and so often works independently of his "little brothers", though he will work with them if he must. Coconuts' name and design are lifted directly from the "Coconuts" badnik of Sonic the Hedgehog 2.
Butt Monkey: Takes abuse most of the time simply for existing despite his rather extreme effort and enthusiasm, getting demoted constantly for mostly nothing...and it's not like Scratch and Grounder are much better off.
The Unfavorite: Gets it much worse than Scratch and Grounder, which is really saying something.
A robotic female hedgehog created by Robotnik to run Sonic into an exhausted state by bending him around her little finger and sending him on impossibly long quests to please her. She has a change of heart when Sonic turns out to genuinely care for her and winds up joining a community of Robotnik's various "junked" robots.
Robotnik's harridan mother, normally held safely away in the "Mobius Home for Really Bizarre Mothers" but who sometimes escapes to harrass her son and everyone else. She looks almost identical to her son, but she's considerably larger (usually twice his size, depending on the scene) and much nastier.
Uncanny Family Resemblance: As stated above, she's a bigger, fatter, ugly, bustier Robotnik in a dress with little girly eyelashes.
An artificial son created by Robotnik to inherit his empire, since the alternative, giving it to Scratch, Grounder and Coconuts, is unthinkable to him. Unfortunately for Robotnik, he turns rebel against him and goes to live with Robotnik's other rejects, where he develops a crush on Breezie.
Double Standard: Abuse, Female on Male: Her entire role in "Zoobotnik" consists of her manhandling Robotnik in what is blatantly sexual assault, including at one point jumping up and down on him in a way similar to dry humping. However, while she's not called on it, it's very clear that it is not okay and Robotnik is actually very afraid of her.
Evil Versus Evil: Her against Mama Robotnik. Katella concedes because she refuses to have her for a mother-in-law.