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At the beginning of your upkeep, you may put a charge counter on Aether Vial.
{T}: You may put a creature card with mana value equal to the number of charge counters on Aether Vial from your hand onto the battlefield.
If Aether Vial leaves the battlefield while its second ability is on the stack, use its last known number of charge counters to determine what you may put from your hand onto the battlefield.
If a card in a player’s hand has {X} in its mana cost, X is considered to be 0.
