I have a few ideas to revise some of the villains from batman, and their origins.
1; Killer Croc
I never liked the idea that Croc suffered from Atavism. Avatism causes a person to be born with traits of an genetic ancestor (A person born with the elongated forehead of a Neanderthal, for example), and it makes no sense for Croc to have reptilian traits from the condition.
I would have him be the victim of a government super soldier program, designed to create human-animal hybrids. He escapes from the facility, but is injured doing so, and is found by a traveling circus. He is taken in by the circus and helps them by becoming part of their sideshow. He gets angry when customers are bullying one of the "freaks", and attacks them, killing them. He runs, with the help of the other "freaks", who are grateful for his help, and heads into the sewers. He lives in the sewers for several years, coming out to steal food and he attacks people who see him, causing legends to grow about the "monster" in the sewers of Gotham City.
Now, don't get me wrong. I love Bane, and his current origin story, but I think there is always room for alternate origins, especially if they are done separately and do not interfere in current ones.
My idea for Bane is to make him a professional wrestler, turned criminal. He is still from Santa Prisca, but instead of being raised in a prison, escapes with him and bring him to America. They settle in Gotham City, he does very in school, but has to leave high school to get a job when his mother becomes sick. He works on the docks, but none of them pay enough, so begins to take part in illegal cage fights. A recruiter for Gotham City Championship Wrestling sees one of his fights and offers him a contract. The recruiter also works for the Falcone Crime Family, and is looking for wrestlers to work for the family. He agrees and begins to work as a wrestler, quickly becoming a star. He wins the GCCW Heavyweight Championship within a year, and completely undefeated, he becomes known as the most dominant force pro wrestling has ever seen.
About 3 years into his title reign, Bane is still on top. However, the Moroni Family's newest star, (name not thought of yet), is better than he is and easily defeats him. The Falcone Family, angry at Bane's loss cut ties with him, only letting him live because of the money he's made for them in the past. Unemployed, and missing the lifestyle that wrestling allowed him to have, Bane looks for ways to get back on top. He eventually is introduced to VENOM, a new form of steroid that was created as part of a failed supersoldier program, and begins using it. He wins back the world title, but eventually the effects of the drug wear off. He goes back to get more, but has to pay 5 times the amount he did before and can't afford it. The Maroni Family, who own the supply of VENON, offer him all he wants, as long as he works for them as an enforcer. He agrees and uses the VENON to get back on top in GCCW, but eventually the use of the drug is too much, and he kills another wrestler in a fit of rage during a match. He is banned from GCCW, but, still addicted to VENON, continues to work for the Maroni family.