From the Comprehensive Rules (Commander 2018 (August 10, 2018))
- 616. Interaction of Replacement and/or Prevention Effects
- 616.1. If two or more replacement and/or prevention effects are attempting to modify the way an event affects an object or player, the affected object’s controller (or its owner if it has no controller) or the affected player chooses one to apply, following the steps listed below. If two or more players have to make these choices at the same time, choices are made in APNAP order (see rule 101.4).
- 616.1a If any of the replacement and/or prevention effects are self-replacement effects (see rule 614.15), one of them must be chosen. If not, proceed to rule 616.1b.
- 616.1b If any of the replacement and/or prevention effects would modify under whose control an object would enter the battlefield, one of them must be chosen. If not, proceed to rule 616.1c.
- 616.1c If any of the replacement and/or prevention effects would cause an object to become a copy of another object as it enters the battlefield, one of them must be chosen. If not, proceed to rule 616.1d.
- 616.1d Any of the applicable replacement and/or prevention effects may be chosen.
- 616.1e Once the chosen effect has been applied, this process is repeated (taking into account only replacement or prevention effects that would now be applicable) until there are no more left to apply.
Example: Two permanents are on the battlefield. One is an enchantment that reads “If a card would be put into a graveyard from anywhere, instead exile it,” and the other is a creature that reads “If [this creature] would die, instead shuffle it into its owner’s library.” If the creature is destroyed, its controller decides which replacement to apply first; the other does nothing.
Example: Essence of the Wild reads “Creatures you control enter the battlefield as a copy of Essence of the Wild.” A player who controls Essence of the Wild casts Rusted Sentinel, which normally enters the battlefield tapped. As it enters the battlefield, the copy effect from Essence of the Wild is applied first. As a result, it no longer has the ability that causes it to enter the battlefield tapped. Rusted Sentinel will enter the battlefield as an untapped copy of Essence of the Wild.
- 616.1f While following the steps in 616.1a–d, one replacement or prevention effect may apply to an event, and another may apply to an event contained within the first event. In this case, the second effect can’t be chosen until after the first effect has been chosen.
Example: A player is instructed to create a token that’s a copy of Voice of All, which has the ability “As Voice of All enters the battlefield, choose a color.” Doubling Season has an ability that reads “If an effect would create one or more tokens under your control, it creates twice that many of those tokens instead.” Because entering the battlefield is an event contained within the event of creating a token, the effect of Doubling Season must be applied first, and then the effects of the two Voice of All tokens may be applied in either order.
- 616.2. A replacement or prevention effect can become applicable to an event as the result of another replacement or prevention effect that modifies the event.
Example: One effect reads “If you would gain life, draw that many cards instead,” and another reads “If you would draw a card, return a card from your graveyard to your hand instead.” Both effects combine (regardless of the order they came into existence): Instead of gaining 1 life, the player puts a card from their graveyard into their hand.