It has complicated text, but in short, you and your opponent just take and return one card each repeatedly
It is easy to gather 3 cards if you use the above same-sex same-name alliance or Hell's Runaway Exchange, so if you put those cards in, it's worth using them together as a combo
Getting four Energy in play can be a challenge, especially in the early game, but its worth the effort as 150 damage can Knock Out most opposing critters
You may cast Mithril Coat even if you don't control any creatures
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They also might be surprised to learn that those cards could hold more value than just childhood memories, authenticators say, with some rare editions reselling for thousands