While its sales aren't quite as high as its console-based counterpart, "Batman: Arkham City Lockdown" has been making waves in Apple's App Store, with players taking control of Batman as he hunts down some of Gotham City's most dangerous fiends. Today, the dark Knight can add one more to target his to-do list.

Warner Bros. Interactive Entertainment and DC Entertainment have released the latest downloadable update for the game, including a new mission that features the return of the Joker's dangerous right hand lady, Harley Quinn. Additionally, the update includes a Bruce Wayne character skin, along with numerous new Achievements for players to earn.

In the mission, Batman works his way through the streets of Gotham to find Harley, facing off against her henchmen in the process, including the powerful Mr. Hammer, a one-armed clown carrying a massive sledgehammer. In the course of the battle, which has to be completed in a certain amount of time, Batman must skillfully use his Batarangs to bring down the maniacally mad girl.

The best part about this update is that, like most App updates, it's available free of charge for those who have already bought the game. You simply need to download it and apply it to your iOs-running device. It's a great addition to an already solid comic book-related app.

"Batman: Arkham City Lockdown" is available now in the App Store.