Rule 359.3.e.9.a

If another spell or ability attempts to reference the number of game objects, players, or zones that a Finalized Chain Item targets, it will include any mistargeted choices, but not any targets that have changed to a non-board zone. Example: When a player moves their Volibear, Furious to an occupied enemy battlefield and combat initiates, Volibear’s attack trigger goes on the chain targeting three of the units at that battlefield. In reaction, the defending player plays Flash moving two of the three units back. That player cannot then target the attack trigger with Repulse, which reads “Choose a friendly unit at a battlefield. Counter an enemy spell or ability that chooses it and no other friendly unit.” If the defending player instead played Heedless Resurrection twice, killing the two units, Repulse can legally target the attack trigger, because two of the targets have changed to a non-board zone.