Rule 603.7a

Delayed triggered abilities come from spells or other abilities that create them on resolution, or are created as the result of a replacement effect being applied. That means 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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