You unlock infinite ammo once you have completed every single level on Agent difficulty. It sounds hard becauseit is hard, it took me ages to do it.

It is quite simple yet difficult. Many people get stuch on moving the pipe and jumping to the next tran car. First, undo the pipe and step back just a little, but not too little. Then, Start running and only jump when the pipe has moved all the way over. Once you land you will feel great and I hope you will think of me. Thank you a whole bunch, bye!