It would be pretty hard to create a champion so frightening and unsettling that people would ban them straight out of fear... How about this?
Doug "Dead Arms" Hensen, the Biophile
In life, Doug Hensen was a serial killer who preyed on young children. Doug began by collecting discarded fetuses from the Zaun abortion clinic where he worked, filling his small and filthy apartment flat with many jars and boxes of fetuses along with various other grisly human articles he could lay his hands on. When the neighbors complained of the stench, Doug was forced to dispose of his disturbing collection, and so he moved on to fresher sources of pleasure. Doug visited the poorest ghettos, hunting for the most vulnerable of Zaun. He would kidnap whole groups of street urchin children and force them to watch as he tortured and murdered their playmates one-by-one while they awaited their own terrible fate. After killing a child, Doug would live out his twisted, often sexual, fantasies with the mutilated corpse.
Doug maintained his secrecy for years, disposing of some of his victims' remains via cannibalism and then throwing the rest down a sewer entrance behind his apartment. The sewer rats quickly learned to gather in anticipation of a meal whenever they heard the sound of Doug pulling the sewer manhole cover open. When the citizens of Zaun finally caught Doug and stormed his apartment, he fled out his back window. In his plight, Doug desperately pulled open the manhole cover and dove inside to escape the furious mob. But at the first sign of Doug's approach, the rats had already gathered in their swarms below, hungering for human flesh. They tore at Doug, tearing skin, muscle, and a few whole fingers from Doug's exposed hands and arms as he tried to beat the rats chewing into his his face and neck. Screaming and bloody, Doug blindly stumbled down the sewer tunnel, wading through the writhing masses. He tumbled off a ledge and into the river of flowing sewage filth. The raw sewage was agony as it mixed into the blood of his open wounds and poured into Doug's rat-bitten, lipless mouth down his scream-gargling throat.
Unfortunately, this was not the end of Doug "Dead Arms" Hensen. There was something special in the Zaun sewage that evening - a chem-baron's private concoction of illegal elixirs. When the mob had stormed down the street to Doug's apartment, the chem-baron's henchmen had panicked and dumped the whole stock of chemicals they were transporting. The chemicals infused with Doug's wicked blood, keeping him from fading into true death as he was drowned and exsanguinated beneath the streets of Zaun.
" ...I need a warm body to put some heat in these cold bones... You'll do, Sweet Cheeks... " - Doug "Dead Arms" Hensen
So he's a zombie rapist. Creepy enough?
He'd look like a ragged zombie with skeletal arms and no skin on his face. He'd be CC focused with a couple abilities that drug and kidnap opponents. He'd probably also have some revive and sustain mechanics, with a playstyle where he's not truly tanky but keeps coming back when you think you've gotten him killed. Anyone want to design a full kit for him?
Ps. No, I don't actually think this is a good champion idea. I am just illustrating what it would be like if there were actually a champion disturbing enough to be banned out of pure "creepiness" factor.