User blog comment:Hylobatidae/help/@comment-5620949-20121118005422

1. The 5 cards show up in the fight is so called Front-Line. They deal 100% to total damage, and they have a probability to use their skills that increases or deceases ATK and DEF. When you use ATK PWR more than these five cards need, the reserve card called Back-Line can participate in the fight. But of course less effecient than the Front Line, only 80% damage. More Info: http://legendofthecryptids.wikia.com/wiki/Battle

2. Lush is expensive because of his high stats for being a rare card. Several cards are limited, you can not get them anymore so they becomes rare. Even their stats are so far useless but still cost a ton of potions.