After you beat Omega Shenron in the GT Saga, continue unlocking new missions in story mode until you get to the Majin Saga. Keep unlocking new missions until you come across the World Tournament missions. One of them lets you play as Android #18. THe mission is to allow Hercule to knock you out of bounds. Unlock the highest difficulty (Z) by buying it in the Warrior's Room for about 10,000 to 30,000 zeni in the black capsule category. Then go back to the mission, set the difficulty to Z, then, when the battle starts, zoom over to the edge, and let him ring you out. Try not to hit him, and if he circles around you, use X and the analog stick to reposition yourself. Let him ring you out, and you will get 60,000 zeni for the Z ranking on the Z difficulty. If he tries using Present Bomb at the start of the battle, restart the mission. Doing this will allow you to get ringed out relatively easy. Repeat to get massive amounts of zeni.
Added by: Goblinaro Nov 17th 2008, ID#31207