After you have Marik resurrect the Winged Dragon of Ra (Battle Mode) you have to go back and have Paradox tell you the location to Pegasus's Castle, but you have to play a game with him. You have to duel 5 of the gaurdian guys inorder reach him, after you duel the fifth one, do not go through the next door ! Go back and save and get you LP back up, then go back, you will have to duel the 5 again, but you will get more Deck Capacity and cards doing this. Repeat until you reach your desired level.