Hidetsugu and Kairi

Flying
When Hidetsugu and Kairi enters, draw three cards, then put two cards from your hand on top of your library in any order.
When Hidetsugu and Kairi dies, exile the top card of your library. Target opponent loses life equal to its mana value. If it's an instant or sorcery card, you may cast it without paying its mana cost.

March of the Machine

Flying
When Hidetsugu and Kairi enters the battlefield, draw three cards, then put two cards from your hand on top of your library in any order.
When Hidetsugu and Kairi dies, exile the top card of your library. Target opponent loses life equal to its mana value. If it's an instant or sorcery card, you may cast it without paying its mana cost.

March of the Machine Promos

If the card has {X} in its mana cost, you must choose 0 as the value of X when casting it without paying its mana cost.

If you cast a card “without paying its mana cost,” you can’t pay any alternative costs. You can, however, pay additional costs. If the card has any mandatory additional costs, those must be paid to cast the card.

The last triggered ability targets the opponent. If that player is an illegal target as the ability tries to resolve, the ability won’t resolve and none of its effects will happen. You won’t exile a card.

The two cards you put on top of your library can be from the three you just drew or ones that were already in your hand.

You choose whether or not to cast the instant or sorcery card as the last triggered ability resolves. If you do, you do so as part of the resolution of that ability. You can’t wait to cast it later in the turn. Timing restrictions based on the card’s type are ignored.