Lots of Money/Good cards
After beating Marik, you will come into the Paradox challenge. Here you will fight 5 duelists one after the other. You have to win to move to the next duelist but every time you beat them they give you a card. Beat the first 4 guys and they will give you kuriboh, time wizard, celtic guardian, and giant soldier of stone.Then lose to the next guy purposefully, and beat the 4 first guys again, etc. Then you can sell the bad cards, and sell or keep the good ones. After you are satisfied beat all 5 duelists.
Added by: NintendoMan!!!!!.. Feb 9th 2008, ID#11761