Rule 121.8

If a spell or ability causes a card to be drawn while another spell is being cast, the drawn card is kept face down until that spell becomes cast (see rule 601.2i) or until the casting process is reversed (see rule 725, “Handling Illegal Actions”). The same is true with relation to another ability being activated. If an effect allows or instructs a player to reveal the card as it’s being drawn, it’s revealed after the spell becomes cast or the ability becomes activated. While face down, the drawn card is considered to have no characteristics and can’t be used to pay any part of the cost of the spell or ability that would require the card to have specific characteristics.

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