i think new cards appearance in old timeline will simply broke the balance.
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LIKEin my opinion, why pot of greed not that broken in the past because there's not that many play / combo you can make with it. in the past broken card is just like yatagarasu :v , nowadays you can let your opponent play alone in the first turn, explaining what they're doing only to wait for your imminent loss. the fact that you can use old deck to face new deck in the current game is enough to make the fact that having new card in the past just too op.