You can no longer buy the original version directly on an Xbox 360 console. Redownloads:
When looking for a Castle Crashers ISO, it is important to understand what the file actually is. An ISO is a disc image—a digital copy of everything contained on a physical disc. However, because Castle Crashers was originally a digital-only XBLA release, it did not have a standard retail disc in many regions. Most "ISO" files for this game are actually converted XBLA containers (XEX or LIVE files) formatted to work with Xbox 360 exploits or emulators. castle crashers iso xbox 360