There are two different classes of responding:
- Responding to an activation (action that uses a Chain).
- Responding to an action that does not use a Chain.
If a card or effect can only be activated in response to an action, but that action cannot be responded to at that time, that card or effect misses the timing.
Responding to a non-activation action
Some cards and effects can only be activated in response to non-activation actions. Both actions performed due to an effect (such as banishing a monster with "Dark Core") and game actions (such conducting the normal draw) can be responded to.
Only the most recent action can be responded to. For example, "Chthonian Blast" can be activated in response to a monster being destroyed by "Dark Hole" or "Gemini Spark" because the monster being destroyed is the last thing to happen, but cannot be activated in response to "Soul Taker" because Life Points are gained after the monster is destroyed. Cards with Problem-Solving Card Text use the conjunctives "and", "also", and "and if you do" to indicate simultaneity, and use "then" to indicate that actions are performed in sequence.
While building a Chain, whatever action occurred before the construction of the Chain is still considered the last thing to happen. For example, if the turn player declares an attack and activates "Rising Energy" in response, their opponent can chain "Mirror Force", because the attack declaration is still considered the last thing to happen (not the discarding action due to "Rising Energy").
Actions that do not go on a Chain can only be responded to, not Chained to. It is incorrect to say that an action that does not go on a Chain is "Chained to".
Responding to an activation
When a card or effect is activated, fast effects with the same or higher Spell Speed can be activated in response, but only if it is the Chain Link immediately above that activation. A card or effect that negates an activation can only do so if it is activated in response to the one it would negate, unless it would negate the entire rest of the Chain (such as "Vanity's Call").
If a card prevents a card from being activated in response to its activation, such as "Night Beam" and "Fire Formation - Gyokkou", then during that Chain the card is only prevented from being activated as the Chain Link immediately after that activation; if another card or effect is Chained to that suppressing card, the target card can be Chained to that other card or effect.