Things You'll Need
Instructions
Select "Mission Start ONI: Sword Base" from the Campaign menu. Under "scoring options" choose "free for all." Under "difficulty," choose "normal."
Take the west ramp (located to your right as the mission starts) to the top as soon as the match begins, then jump to the top of the north wall. Take this path south toward a gate.
Enter the garage and head straight to the western wall. Stand over suitcase and hold the "X" button to acquire the the "Target Locator."
Press "start." Choose "set checkpoint" from the pause menu.
Move to the south gate (opposite from where you entered) and aim the target locator at the street ahead as enemies begin to approach. Hold the "R" trigger to fire. The resultant blast will give you a few hundred to several thousand credits depending on your rank and the medals you've already accumulated.
Press the "start" button and select "restart from last checkpoint." Again, fire on the group of approaching enemies to rack up even more credits. You can do this over and over to acquire thousands of credits in just a couple minutes.