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Hello guys, I have been playing the kethis combo deck and I notice that I can play infinite mox amber. However in the official page this card has this rule:

"Kethis’s last ability affects only legendary cards that are in your graveyard at the time it resolves. Legendary cards put into your graveyard later in the turn won’t gain the ability. If you play a legendary card and it returns to your graveyard, it won’t have the ability anymore."

So basically you have to pay the cost again and again everytime you want to recast a mox amber that returns to the graveyard.