The Joker's Carnival

The Joker's Carnival is a combat challenge map in Batman: Arkham City. The challenge is timed, but consists of unlimited waves of enemies, and the player is required to constantly bank their points to add to their time. It is one of the three DLC challenge maps that are not part of any character DLC, with the others being Iceberg Lounge VIP Room and Batcave.

Medals

 * 100,000 points
 * 500,000 points
 * 1,000,000 points

Timer System
This challenge features a unique timer system, starting from 3 minutes, which can be extended by defeating enemies. On the right side of the screen, there is a new HUD item which shows the players current level and points, and how much time banking said points would add. Every new level reached spawns more difficult enemies. Levels are advanced by landing attacks, and are reset whenever the player takes a hit or banks the time & points for that level. All attacks add the same value to level advancement as they do to combo count.

Level info

 * Not an actual level. When 220 blows are landed, time and points are automatically banked, and the player's level is reset to 0.

Joker Fight
If the player manages to reach a 100x combo, Joker will jump into the arena, and become an enemy. He can be knocked out, and has around as much health as an Armored Henchman. Naturally, Joker's commentary will end upon joining the fight.

Trivia

 * This is one of the three challenge maps in Batman: Arkham City in which The Riddler isn't providing the commentary, being replaced by The Joker. The other maps are Iceberg Lounge VIP Room, which features the Penguin, and The Batcave, where the Batcomputer informs enemies.
 * If the player chooses to play as Robin, Joker might mention "Didn't I kill you already?" This is a reference to the second Robin, Jason Todd.
 * A criminal sings the opening of 1966 TV show.
 * This is widely considered by fans to be one of the hardest challenge maps in the Arkham games, others include the extreme versions of Top of the World and End of the Line.