Prince of Persia: The Two Thrones

This is the very last trophy you'll get (along with the platinum). You should start farming credits once you finish your last playthrough as they accumulate during all your playtime. Sand credits are found inside objects, inside little golden chests scattered around and once you kill enemies and bosses.

Here's a more effective way:

After beating the Vizier, there will be a section called "Mind Realm" where you have to complete one last climbing part. Once this ends the game will ask if you want to save. Do so and once back on the main menu, reload your save and complete this last section again. Every time you do, you'll be awarded with 700 credits on hard. Repeat as many times as needed.