This is actually very possible as long as you follow the directions. First, you must have Ultimate Baseball Kid, Macro Cosmos, Molten Destruction and the most important card is DNA Transplant. With this, fill out your Monster Card Zone and wait for a few turns as your opponent will fill out the zones too. When both fields are filled with monsters, check the ATK of Ultimate Baseball Kid. And you should have 10,000 ATK exact! Hope this helps ^_^.
When you rent 3 cards,put them in your deck then go back to the rental counter and go to your rental cards and press triangle,chose selected card menu and press empty card tab or somthing like that and your cards will be gone.Keep on repeating this and get all the cards you want and you wont have to pay money for it either!