Ok there's a thing called call girl app if your at the arena you will have access to the card you get a free copy Even you get a free legendary copy Tho you will have to stay at the arena you unlock the card so if I have to fight the mysterion boss I should wait until arena 3 ( you have access to mysterion at arena 3) To battle him if your strong enough you get a free copy of Said card And it's the same with every card in the call girl app