I notice you're asking about a "Castle Crashers PSP ISO" — however, . The game originally launched on Xbox Live Arcade (2008), then later came to PS3, PC, and modern consoles (Switch, PS4, Xbox One), but not PSP or PS Vita.
The PS Vita is backwards compatible with PSP digital titles, but more importantly, Castle Crashers has a native (released 2014). It runs at native resolution, includes the Back Off Barbarian mini-game, and supports ad-hoc co-op. You can find a maidump or Vitamin backup of the Vita version, but the keyword there is Vita , not PSP. castle crashers psp iso upd
: You can play the full, official versions (including the Remastered edition) on PlayStation , Nintendo Switch , and Steam . Quick Guide to Unlocking Classic Characters Castle Crashers was never officially released for the