Rule 603.7a

Delayed triggered abilities are created during the resolution of spells or abilities, as the result of a replacement effect being applied, or as a result of a static ability that allows a player to take an action. A delayed triggered ability won’t trigger until it has actually been created, even if its trigger event occurred just beforehand. Other events that happen earlier may make the trigger event impossible. Example: Part of an effect reads “When this creature leaves the battlefield,” but the creature in question leaves the battlefield before the spell or ability creating the effect resolves. In this case, the delayed ability never triggers. Example: If an effect reads “When this creature becomes untapped” and the named creature becomes untapped before the effect resolves, the ability waits for the next time that creature untaps.

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