To choose a card in your hand, clearly separate it from the rest of your hand without revealing it.

Although you may choose a land card in your hand, you won’t be able to play it even if the player guessed wrong.

If you don’t cast the card, either because the player guessed right or because you choose not to cast it, you don’t have to reveal it. Your opponent won’t know the reason you didn’t cast the card.

If the card has in its mana cost, X is 0.

You cast the card in your hand as part of the resolution of the triggered ability. Timing restrictions based on the card’s type (such as creature or sorcery) are ignored. Other restrictions, such as “Cast [this card] only during combat,” are not.

If you cast a card “without paying its mana cost,” you can’t pay any alternative costs. Notably, you can’t cast a card with bestow as an Aura this way. You can, however, pay additional costs, such as kicker costs. If the card has any mandatory additional costs, you must pay those.

If the card is a split card, it has two converted mana costs, one for each half. If both converted mana costs are greater than 4 or if both are not, the opponent must guess appropriately to be correct. If one converted mana cost is greater than 4 and one is not, guessing that the card’s converted mana cost is greater than 4 is correct, and guessing that the card’s converted mana cost isn’t greater than 4 is wrong. If the player guesses wrong and you cast a split card this way, you may cast either half (or both halves if the card has fuse), no matter what its converted mana cost is.