The PC version of Dark Souls, dubbed the "Prepare to Die" edition, added several hours of new content in addition to balance tweaks, frame rate fixes and more. Now those changes have come to PS3 and Xbox 360 in the form of the $15 "Artorias of the Abyss" expansion.
"Artorias" adds the new areas, enemies and equipment from the PC version, along with the various tweaks and fixes—including a substantial change to how a certain overused ring works, making the game's unique PVP a much more balanced affair.
In addition, there's now an arena mode that should easily facilitate PVP in 1v1, 2v2 and 4-player free-for-all matches.
As Eurogamer points out, there's a chance you'll have to play through a significant chunk of the game in order to access the new content, especially if you've just started a new game plus or you plan on starting a brand new character. It's definitely worth it, though—check out our Dark Souls: Prepare to Die review if you've got any doubts.