Intervene | Magic: The Gathering
Formats Intervene is Legal in
Official Oracle Text for Intervene
—Karn, silver golem
Official Rulings for Intervene
10/4/2004 : Intervene can only target a spell that is currently targeting a creature.
10/4/2004 : It means "targeting at least one creature" not "exactly one creature".
10/4/2004 : If the spell's target leaves the battlefield before this spell resolves, Intervene will be countered since it no longer targets a spell that targets a creature.