First choose Gomamon, then get the auto digivolve in the beggining of the match under the brindge by slamming it and breaking it. Then you will be Ikkakumon. Keep up a fight and gather as much blue orbs until you can digivolve once more. After that go on the left and run and stop to the wall where you can jump on, but dont go up. Stay at the wall position and turn to face the open side. Then keep pressing the square button to make him smash his hammer and send a never ending chain of waves and noone can approch you with out dying, and then if someone approaches from the top the press up + square to throw a giant hammer.