This article contains spoilers for Detective Comics #1026 by Peter J. Tomasi, Brad Walker, Andrew Hennessy.
Killer Croc is its mayor. Let's face it, nobody risk-averse would ever choose to live in Gotham City. Where most cities enjoy (or endure) spring, summer, autumn, and winter, Gotham tends to experience a cycle of escalating violence that periodically leads to the city being overrun by some costumed lunatic or another. Last year Bane got to take over Gotham for a while; this year it's the Joker's turn.
The Clown Prince of Crime has certainly done a good job in the "Joker has successfully stolen the Wayne fortune, and he's undermined the GD from this newfound position of wealth and power. Batman and his recovering allies are desperately trying to find a way to turn back the tide of madness. Even Gotham's other criminals have hunkered down, waiting for the chaos to end.
In this week's Detective Comics #1026, Batman learns there have been unexpected casualties - and the Joker's insanity has unwittingly created a new Monstertown in the sewers beneath Gotham. It seems the Joker's clowns, looking to spread some joy, hit ACE Chemicals, and flooded the place with toxic chemicals. It all flooded down into the sewers - where a gang of conscientious objectors had hidden for safety away from the war between the Jokers and the Bats. They were all soaked in the chemicals and would have been drowned if not for the intervention of Killer Croc, who had also sought sanctuary in the sewers. Hideously mutated, they became Killer Croc's new people, the first citizens of Monstertown, and Killer Croc declared himself their mayor.
Monstertown has only a small population right now - there are only six residents, named Ratty Riz, Hardback, Gup, Ally, Garter, and Bandit - but they're planned on explosive population growth. They've been kidnapping people from the surface, planning to drop them into the chemical soup now running through Gotham's sewers, figuring they can create yet more monsters. Unfortunately, Batman's analytical tools swiftly tell him nobody else could survive such extended exposure because these chemicals are seriously toxic.
Naturally, there's no way Batman can allow Monstertown to remain; not least because Killer Croc already has over a half-dozen captives he's about to unwittingly kill. But the unanswered question is the most disturbing; what will happen to this toxic sewage once the dust has settled from the "Joker War?" Gotham is going to need to cash out on some major clear-up.
