I'm picking more-so characters who tried to erase a group of people than just trying to destroy the world. Destroying the world does kill everyone, but they would have destroyed it either if people were there or not. To put it simply, the ultimate goal is not genocide, it just comes with it. Trying to kill everyone does count, because everyone is a group of people, especially from an alien perspective.
This is not supposed to poke fun at genocide, it is poking fun at the absurdity of Sonic characters comitting it. Enjoy.
Of course, I couldn't pick any one else. Besides his actions endangering the lives of millions, and actually killing a few thousands with stuff like the Perfect Chaos/Prison Island incidents, he actually succeeded at wiping out the furries in some media. In the Archie comics, the "main" Dr. Eggman (there are multiple) actually nuked the entirety of Mobius, with the intent to kill all Mobians. Not only that, after he did it, he hopped into another dimension to do it again. God he's amazing.
Ahaha, yes I had to use this image. They are this high because they are reponsible for 2, probably more. I will start with the simpler one. In Fleetway's Sonic the Comic, there was a dinosaur race called the Kohenyu. There were a lot of females, but very few males. The males, being the slowest, were all hunted and killed by the echidnas, dooming the race into extinction. Very much later, dinosaur ghosts will haunt Knuckles in some stories because of this, which is rather amusing. And yeah those dinosaurs could talk.
Now for the more difficult one. In the Archie comics, there was a war waged between the Order of Ixis and the Echidnas of Albion, this was called the Forgotten War. Basically, the Order of Ixis were a bunch of wizards led by a guy called Mammoth Mogul, and because they tried to conquer the world, the echidnas said "hell no" and started a war. Albion is the home city of echidnas and it was super technologically advanced bla bla bla. At first, the Albion Knights of Aurora (basically the army) were losing the war, so scientists in a Downunda (Australia) colony decided to experiment on civillians and commit crimes against nature to create bio-weapons and such. By genetically experimenting on the tribe of tasmanian devils, they made a group of them into mindless Mobini devil dogs. Mobians are pretty much furries, Mobini are regular animals like flickies and your dog and stuff. In each subsequent generation of tasmanian devils, the prevalence of children birthed devil dogs increased. Until in one generation, only one Mobian devil was born, dooming Mobian tasmanian devils to extinction. Echidna war crimes, man.
Obviously, the events of Sonic Adventure 2. Even if the memories implanted in him were fake, Shadow still tried to wipe out humanity to fullfill Maria's wish. I know Gerald Robotnik and G.U.N are arguably guiltier of this, but Shadow has a larger kill count. He also killed the entirety of the Black Arms, barring one individual in the Archie comics. It doesn't really matter if a species was threatening the earth, it still counts. As a bonus, I'm adding Sonic the Comic Online. A "bonus" because these aren't officially licensed, even if considered widely to be the canon continuation of STC. Anyways, there, Shadow destroyed the Special Zone, killing millions. Can you tell I love this guy?
Here we've reached the "attempted genocide" tier. Why them but not shit like Solaris, Dark Gaia, etc? Well, because of the intent. As I established in the intro, destroying the world and trying to kill everyone are two different things. Anyways. These guys tried to paralyze all living beings on Earth/Mobius with a gaz to eat them and multiply. In the Archie comics, they even tried to do it twice, though failing both times and going almost extinct in the process. They are here because of the scale of their attempts.
So in the Archie comics, Dr. Robotnik can roboticize Mobians. Going beyond just an animal being used as a battery, it's full on becoming a mindless robot slave permanently. After a series of events, a group of roboticized Mobians, dubbed Robians, could regain their free will despite their state. King Max, gone mad and delirious because of his half crystallized state (magic wizard stuff don't think about it too hard), ordered the killing of every single Robian out of a fear they go rogue. How this guy like him, espcially in such a state, is being put in a position of power is beyond me. Thankfully this plan didn't get executed, especially since all Robians got de-reboticized later on. King Max would have killed thousands of innocents, including Sonic's own parents. Of course, Ken Penders justified these actions as "pragmatic".