This list is based on how much trouble they give Batman, not how strong they are or their skills. Only their skills on making Batman's life a living hell. (I mean that's what they are trying to do). Most Batman villains aren't on here because they are so easy for Batman to deal with, or at least aren't big threats
After taking a potion (his biggest weakness) Langstrom will turn into a bat the size of a man, and with enhanced senses and strength. Man-Bat mostly inflicts terror in the people of Gotham before Batman steps in. Also the first villain Batman fights in Batman: The Animated Series.
An assassin who only kills when hired, but he never misses. Deadshot also tattoos all of his victims onto his body to always remind himself how many lives he has taken. Will Smith is playing him in the upcoming Suicide Squad movie. And was also in Arkham City.
Slade Wilson, an enhanced mercenary with only his left eye, breed to kill and apart of the Suicide Squad. Batman always seems stronger. I wonder why?
#16 Black Mask
A man like the Penguin, who wants to rule Gotham with an iron fist. Owner of Sionis industries, and leader of his mob. His mask is seared to his face.
#15 Killer Croc
Born a disfigured boy, Jones was laughed at and put into a circus. His strength and willingness to be put under for further experimentation, has made him more animal than man. Though his strength is amazing, his brain is scattered from the experiments making him easier to stop and yet far more dangerous.
Basil Karlo, pissed that he didn't get a part in a horro movie of the same name, used his acting skills after being exposed to a chemical to trick people and steal. Able to change into anyone right down to their DNA, even able to copy their powers if they had any. Able to change size, alter his clay body and density, superhuman strength, durability and even develops a toxic touch.
Someone who used to work for Wayne Enterprises, Edward Nygma uses his riddles and his smarts to steal. Though he is in Arkham Asylum more often than not, creating new ways to escape his cell when the time is right.
#12 Poison Ivy
Pamela Isley, exposed to one of her own chemicals from all her botany knowledge. Able to control plants by manipulating them, her body is toxic, use pheromones to control men and women alike and is immune to all bacteria, poisons and toxins. (Not too be confused with Uma Thurman)
Dr. Crane is a genius, entranced with the aspect of the emotion Fear while being afraid of most things. Crane developed a fear-toxin, a gas or serum that shows people their biggest fears, and usually kills them (unless your batman).
Harvey Dent, a Gotham City district attorney (and a good friend of Bruce Wayne), had acid thrown on half his face by one of the criminals he had put away. The acid changed his face and his mind, turning him into Two-Face, a criminal with two personalities and one that uses a coin to determine his victims fate.
A rich evil mastermind, that just wants all the money in the world (he's a gambler at heart), and a leader of his mob/gang. Oh and he has a weird proclivity for penguins.
#8 Mister Freeze
Victor Friese a scientist infatuated with Nora Fields (who actually isn't his wife he's just crazy), a woman frozen in a cyrogenic stasis tube suffering from cancer. While working for Wayne Enterprises, he got mad at his boss Bruce Wayne, throwing a chair at a pipe that blew cyro fluid at him. He had to create a suit so that he could survive in regular temperatures. Mr. Freeze, is a Genius and has a cold gun that can freeze anything.
#7 Hugo Strange
A smart doctor, who used his genius intellect to determine that Batman was Bruce Wayne, so he uses this knowledge to hang it over Batman's head to always keep him off his game.
#6 Harley Quinn
Harleen Quinzel a psychiatrist at Arkham Asylum that was assigned to The Joker. Soon after she became infatuated with him, as he twisted her mind to think that he was in love with her and now she's in love with him. She'll do anything to impress him. Though she has no powers like her lover, she is an expert gymnast and has an abnormally strong strength in her limbs.
The man who literally broke Batman's back, and is one of Batman's hardest foes to fight, face to face. Powered by the Venom serum to give him superhuman strength, and durability. Raised by the mob his dad ruled, and thrown in jail at a young age for his fathers' crimes.
Childhood friend Thomas Elliot, jealous of Bruce and his good fortune (even killing his own parents to be an orphan like Bruce). Wanting his money and his life, Thomas went through plastic surgery to look like a clone of Bruce Wayne. Now he terrorizes Batman, as he also knows that he is Bruce Wayne because of how closely he followed Bruce's life.
#3 Ra's Al Ghul
The Demon's Head, and leader of The League of Assassins wants to make a better world, even if that means killing everyone in it. Ra's has always wanted Batman to take over his position (batman doesn't kill though), as his Lazarus Pit had taken a toll on his mind and body after living for over 600 years. Also wanting him to marry his daughter Talia (she took Bruce's blood to have Damain be his son). Having Batman take over his role has always been something I wish the writers would make happen even for just a story arc in the comics.
Selina Kyle aka Catwoman, a woman who wants nothing more than to get rich and have Batman love her. Their sexual and crime fighting relationships has always been crazy and unpredictable. But always fun. Selina Kyle is also one of the few criminals who has ever known his secret identity, and one of the few who has one as well.
A man who started off a hero as the Red Hood (not Jason Todd), then fell into a bat of acid changing his face and mind forever. The complete opposite of Batman, he just loves to kill for the laughs, and the fun. Also the only or one of the only one to get inside Batman's head and mess him up with his insanity. Also he thinks that knowing who Batman really is will make it less fun, so he doesn't care about finding out who hides behind the mask. They complete one another, one cannot survive without the other.