Just out of curiosity, how familiar are you with the Ace Attorney series? There are around three characters that I think meet the criteria for Complete Monster that haven't been listed yet, though I of course want to hear your thoughts on them. I'm only going to be going over one for now as he always stuck out to me as being among the nastiest of the series' villains and it always bothered me that he was cut back at TV Tropes: Redd White.
Hailing from the first game in the series, Redd White is a CEO who at first seems like a goofy, flamboyant man and comes off as merely obnoxious, but the man has a much darker side to him. In reality, his company Bluecorp is more or less a company that specializes in blackmail: he obtains information on powerful individuals and companies that would ruin them if it got out to the public and uses them to do his bidding. Many of the people he has blackmailed have committed suicide, which Redd couldn't give a damn about as long as he gets to line his pockets with tons of money and lord it over everyone around him. Whenever the protagonist Phoenix Wright's mentor Mia Fey tries to take his company down, he learns that she's onto him and murders her for her trouble and goes on to create false evidence that makes her kid sister Maya the prime suspect, though he later shifts the blame onto Phoenix himself whenever Phoenix confronts him personally. And because Redd has dirt on the chief prosecutor and possibly the Judge himself, he almost succeeds in getting Phoenix acquitted before he's able to make a comeback and present the evidence showing that not only did Redd murder Mia, but that he was responsible for the suicides of many others as well. It should also be noted that in the past, he leaked information that a spirit medium (Who was Mia and Maya's mother) was assisting in the investigation of a murder to the public, destroying not just the medium's reputation, but her entire family name as well.
In conclusion, Redd's crimes consist of blackmailing countless individuals, driving many of those same people to suicide, soiling the good name of a spirit medium clan, murdering a woman who sought to expose his illicit activities, and attempting to pin the murder on her teenage sister and later her apprentice. All in all, he has one hell of a rap sheet, and I'd make the claim that he's up there with the series' nastiest villains (including Manfred von Karma, who he shares the same game with). He lacks any and all redeeming features, as he only cares about himself and the money and power he can aquire, and knows damn well that the law can't touch him and demonstrates it by punching Phoenix and is able to have him put on trial just by his command alone.
I feel he's an easy keep, though I wonder what your stance on him is.