#20 - The Cavalier

First Appearance - Detective Comics #81 (Nov 1943)

Mortimer Drake was a man of exotic and idiosyncratic taste. When he found himself unable to purchase more exotic valuables for his collection legally, he resorted to theft. Donning a costume resembling that of a Musketeer, he called himself the Cavalier. His course of actions ultimately brought him into conflict with Batman and Robin. Drake matched wits against Batman and Robin several times, and escaped them in each encounter, but Batman was able to deduce the Cavalier's identity, leading to Drake's eventual imprisonment.

#19 - The Calculator

First Appearance - Detective Comics #463

The origins of the Calculator and the advanced technology that he used are unknown. He was known to have had one conflict with Mikaal Tomas, the alien Starman, before disappearing for years. When he returned, he began to progressively attack the Justice League of America, allowing them to defeat him once so his computer could deduce their methods, and then went on to defeat them on their second encounter.

The Calculator continued his spree in Gotham City, and was defeated by Batman, but quickly escaped and headed to Central City. There the entire JLA that he had defeated came to take him down, but he had prepared for this, and was able to defeat them. But he had not prepared for Batman entirely. Batman led Calculator into a trap by predicting how Calculator would try to counter him, and was able to defeat the villain and send him to jail.

#18 - The Spinner

First Appearance - Batman 129 (1960)

A villain whose main weapon was a giant spinning top. Very exciting stuff.

#17 - Blockbuster

First Appearance - Detective Comics #345 (Nov. 1965)

The first Blockbuster was Mark Desmond, a chemist who desired to increase his physical strength. Experimenting on himself, he succeeded in making himself stronger and taller, but a side-effect of the process became almost mindlessly aggressive. The mentally debilitated Desmond was cared for by his brother Roland, a local criminal, who kept their mother from discovering what Mark had done to himself. Roland manipulated his brother into committing crimes on his behalf until they came into conflict with Batman and Robin. Roland Desmond became the second Blockbuster after a severe illness forced him to be treated with experimental steroids. Like his brother Mark, Roland became a child-minded super-strong monster.

#16 - Killer Croc

First Appearance - Detective Comics #523 (February 1983)

Waylon Jones is born with a medical condition that caused him to grow progressively more like a crocodile. In the comics his intelligence level has varied from competent schemer to berserk monster. In his original appearances, he resembled a powerfully-built man covered entirely in green scales. However, his disease has slowly robbed him of identifiable human traits.

#15 - The Eraser

First Appearance - Batman #188 (December 1966)

Lenny Fiasco was a college classmate of Bruce Wayne (Batman), and was continually mocked by his fellow students for all the mistakes he made in class. The few people who remembered Lenny always pictured him with eraser in hand, correcting his mistakes. The only girl Lenny ever wanted was Celia Smith, and he planned to take her to the school's ice carnival. Lenny was crushed when she chose to go with Bruce Wayne. Feeling quite bitter he turned to a life of crime, developing an eraser costume that could eliminate all evidence from a crime scene. He took out advertisements as the Eraser in The Secret Underground, a periodical aimed at Gotham City's small-time criminals. He did a commendable job, and the police were baffled at the lack of clues at a series of bank robberies.

#14 - Bane

First Appearance - Batman: Vengeance of Bane #1 (January 1993)

"Originally intended as a "dark mirror" of the highly disciplined and multi-skilled pulp hero Doc Savage, Bane spends his childhood in a hellish prison on the corrupt island nation of Santa Prisca. He develops superhuman strength through a forced experiment involving the drug Venom. Although his dependency on Venom is an immense weakness, Bane has been one of Batman's most intelligent and physically powerful foes. He is best known for breaking Batman's back in the "Knightfall" story arc."