Costs

There is no official term for this. This is a fan-term used to describe when an action needs to be performed in order to resolve the rest of the following effect. However, the detailed rulebook specifically lists these effects.

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All "costs" are optional, but are required to be done in order to perform the following actions afterwards.

Effect Structure

The three structures are used to define a cost in English:

• "By doing <X>, do <Y>"
• "You may do <X> to <Y>"
• "You may do <Y> by doing <X>"

All three of these are used when defining costs in the Digimon Card Game. There is no substantial difference between the three structures gameplay-wise. However, some cards may be worded "By doing <X>, you may do <Y>" which causes both the cost and the following effect to become optional.

All of these effects are written the same way in Japanese using "By doing <X>, do <Y>".

General Rules

When activating an effect like this, you will choose to perform <X> in order to perform the following <Y>. In all cases performing <X> is optional if you would prefer not to do <Y>. If an effect has a [Once Per Turn] or a similar activation limit, choosing not to pay the cost or being unable to pay the cost will result in the effect not activating.

Additionally, you are allowed to perform <X> even if you would be unable to execute <Y>. If you do so, this will still count towards the [Once Per Turn] or activation limit. But in most cases it is mandatory to perform <Y> after performing <X> unless otherwise specified.

Rulings

1. Q: Is it optional to do <X> for "By doing <X>, do <Y>"?

   A: Yes, it is always optional to do <X> for costs. However, you will have to do <Y> after doing <X> unless stated otherwise.¹
2. Q: Do I have to be able to do <Y> in order to do <X>?

   A: No, however you should try to do as much as possible for <Y> if you do <X>.¹
3. Q: Can I choose not to do <Y> after doing <X>?

   A: Unless it is specified that it is optional to do <Y>, you must do <Y> as much as possible after doing <X>.¹
4. Q: My "By doing <X>, do <Y>" effect has a [Once Per Turn]. If I choose not to do <X>, can I still activate it again later that turn?

   A: Yes, if you do not do <X> the effect will not be activated.¹
5. Q: I have an effect that says "By doing <X>, do <Y>. Then, <Z>.". Can I still do <Z> without doing <X>?

   A: No, you must do <X> in order to do <Z>.²

Sources

• Detailed Rules Explanation

1. Detailed Rules Explanation
2. Carddass Email English 12/10/2021: Mummymon Optional Difference