各対戦相手はそれぞれ、これにより追放したカードのマナ総量の合計が5以上になるまで、自分のライブラリーの一番上から1枚ずつ追放していく。ターン終了時まで、あなたはこれにより追放されているカードを、マナ・コストを支払うことなく唱えてもよい。
If a spell you cast has
in its mana cost, you must choose 0 as the value of X when casting it without paying its mana cost.
Since you are using an alternative cost to cast the spells, you can't pay any other alternative costs. You can, however, pay additional costs, such as kicker costs. If the card has any mandatory additional costs, you must pay those.
If a card in a library has
in its mana cost, X is 0 for the purpose of determining its mana value.