In card texts (abilities), you can see a single word, but important when you are resolving an automatic/activated ability; that is, "then" (さらに Sarani).
This word appears following a full stop, and thus starting of a new effect. In this case, there will be a text previously written, and if that text prior to it has a requirement stated, that means the effect that starts with "then" can only be resolved if the previous requirement has been met.
- A simple example: Carapace Mutant Deity, Machining Destroyer
[ACT](VC)[1/Turn]:[Counter Blast (1)-card with "Machining" in its card name] If you have a heart card with "Machining" in its card name, choose one of your opponent's rear-guards, and that unit cannot [Stand] during your opponent's next stand phase. Then, if the number of rear-guards you have with "Machining" in its card name is four or more, choose one of your opponent's vanguards, and that unit cannot [Stand] during your opponent's next stand phase.
As you can see, the effect that starts with "then" can only be resolved if you have a certain heart card. Otherwise, you cannot resolve it. In other words, this effect requires that the initial requirement is first fulfilled. However, the actions written after the requirement are not required to be performed, but the next effect only need have met the requirement about the heart card.
The same happens when an effect would say "If you have A, do B. Then, do D".
However, there are other cases where no "then" is present at the start of a new effect, while there is a requirement written at the start of the ability. This means the effect without "then" do not require that initial requirement. You can resolve that effect by paying the ability's cost even if the initial requirement is not met. This is because of this effect without "then" is not part of the previous effect that ended with a full stop. In such case, the text remains within the same effect as long as it is in the same line before the next succeeding full stop.
- A simple example: Helldeity Seal Dragon, Crossorigin
[ACT](VC)[1/Turn]:[Counter Blast (1) & Choose a face down card from your G zone, and turn it face up] If you have a heart card with "Seal Dragon" in its card name, for each face up card named "Helldeity Seal Dragon, Crossorigin" in your G zone choose up to one of your opponent's rear-guards, and retire it. Your opponent reveals four cards from the top of his or her deck, and chooses a grade 2 card from among them for each unit put into the drop zone with this effect. Your opponent calls the chosen cards to separate open (RC), and shuffles his or her deck. If your opponent has two or more grade 2 rear-guards, this unit gets [Critical]+1 until end of turn.
As you can see, no "then" after the blue text. That means the effects written after a full stop must be resolved after paying the ability's cost, even the "if you have a heart card..." requirement is not met. But on the other hand, the effect within the requirement cannot be resolved. Even so, if a portion of the effect that needs to be resolved is not possible, it will not do anything, since the previous effect not was done. In this game, you or your opponent resolve that kind of effects as much as possible to do.