Okay, is this a retcon? On Chapter 2 it is explained that all his cards work on a cooldown timer mechanic. When he uses a card it enters cooldown and you can't summon it again until that's over. The higher the rarity, the longer the cooldown. For summon creature cards, the creatures don't die. They just return to card form and then cooldown before they can be summoned again. Why is MC saying he can no longer use the cards he used to kill the Demon God?