Take a very powerful summon card, such as a Red Dragon or a White Tiger. Put it in a small deck including two or three copies of the card, and four Sea Monks. Go to a difficult level. Use the card, restore it with a Sea Monk, then use it again, then use another Sea Monk. It should restore the Sea Monk you already used and the powerful card. This allows you to use the same card repeatedly, even if you only have one of it.