奔流の機械巨人
Artifact Creature — Construct
瞬速
このクリーチャーが戦場に出たとき、あなたの墓地にあるインスタント・カード１枚を対象とする。それを、マナ・コストを支払うことなく唱えてもよい。その呪文があなたの墓地に置かれるなら、代わりにそれを追放する。
Illustrated by
Final Fantasy Commander#272RareJapaneseLegality
Rulings
If you cast the card, you do so as part of the resolution of Torrential Gearhulk’s triggered ability. You can’t wait to cast it later in the turn. Timing restrictions (such as “Cast [this card] only during combat”) still apply.
If you cast a card “without paying its mana cost,” you can’t choose to cast it for any alternative costs, such as emerge costs. You can, however, pay additional costs. If the card has any mandatory additional costs, such as that of Incendiary Sabotage, you must pay those to cast the card.
If the card has 
in its mana cost, you must choose 0 as the value of X when casting it without paying its mana cost.