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You may choose not to untap Coffin Queen during your untap step.
{2}{B}, {T}: Put target creature card from a graveyard onto the battlefield under your control. When Coffin Queen becomes untapped or you lose control of Coffin Queen, exile that creature.
If Coffin Queen leaves the battlefield before its ability resolves, the delayed trigger condition can never be fulfilled, so the creature will not be exiled. If Coffin Queen is untapped when its ability resolves, the creature will not be exiled until the next time Coffin Queen becomes untapped.
If the creature put onto the battlefield leaves the battlefield, the tracking effect ends and the creature will no longer be exiled if something happens to the Coffin Queen.
If the creature put onto the battlefield phases out, the tracking effect continues when it phases back in if the Coffin Queen is still on the battlefield. If the Queen left the battlefield while the creature was phased out, the creature phases in as normal.
