Here is another Proposal Overlord let me borrow.
What is the work?
The Archie comics version of TMNT that ran from 1988 to 1996 had started off as an adaption of the 1987 cartoon, but quickly became its own continuity and became one of the darker things Archie ever published. The villains were allowed to be more evil then the 1987 cartoon. Specifically Krang wipes out a species of aliens in a flash back. Villains created for the comic like Mr. Null and Queen Maligna are pretty nasty, given how light hearted the comics were at times (at had a very cartoonish art style). Maligna was a Hive Queen who killed one of her own children for petty reasons. Mr. Null didn't seem to care about anyone but himself.
Who is Mr. Null? What has he done?
Mr. Null was a villain created for the Archie TMNT series. He was an odd character to say the least, a bit of an over top the Straw Character. He started off as a faceless Corrupt Corporate Executive who ran several environmentally destructive and immoral businesses. The Turtles first encounter one of enterprises, a mining operation that was using a remote South American tribe as slave labor. He ran another business where dumped toxic waste in the ocean. However he doesn't make his first full appearance until he decides to sell the Earth to a bunch of genocidal insect like aliens that want to destroy the human race and make the Earth habitable for them. They send down eggs with their young larvae that hatch and start eating everything in their path. Null is helping these aliens, because he thinks he can make more profits by taking his business off world and make it intergalactic. He also find out he is part demon, with little horns growing out of his head. After that alien invasion is thrawted by both the Turtles and their allies, the Mighty Mutanimals, Null wanted revenge on them. He gained control over the Horsemen of the Apocalypse and used them to capture the Turtles and the Mutanimals. He planned on killing them by slowly electrocuting them, wanted to force one of his former henchman who betrayed him for moral reasons, to pull the switch that would kill them. Null is also a real creep, despite the name the Mutanimals had humans as members and associates and Null would often say he would rather have the female captives become part of his "harem" rather then be killed. After Null was defeated again, he set up an ambush where his cyborg henchmen managed to kill most of the Mutanimals. Mondo Gecko (who was originally human) had a human girlfriend that Null mind raped and brain washed, turning her into his slave (she wears a far more reveling outfit and calls master, it is heavily implied that she is his Sex Slave). He tries to help the same group of aliens destroy humanity again, thinking he could succeed with the Mutanimals out of the way.
Is he heinous by the standards of the story?
He has got some decent competition, Krang is presented as far more ruthless and even genocidal in this series, Queen Maligna, the alien he sold Earth to was a genocidal tyrant that wanted to destroy humanity. However Null aided Maligna in her schemes for selfish reasons and had his own crimes, which include slavery, both sexual and labor and just general sadism.
Any Freudian Excuse or other mitigating factors?
His motives range from greed, lust and For the Evulz, so he has no sympathetic motives and no Freudian Excuse. The only thing that could be mitigating is his nature, he is a demon who seems to become more demonic and less human with every evil act he commits, his true nature is ambiguous (there are hints he may Satan, but that is never confirmed) and the comic never comes out and says he has no moral agency. Do we assume demons have no moral agency?
Null is a bit of tricky character to judge, he is very hands off, content to allow his allies and minions to do most of his dirty work for him and is true nature is ambiguous. He is also a bit of an over the top Straw Character. But he is still a very nasty villain in a fairly light hearted series.
For me (PokemonMasterH), I'd say yes.