419.8c Some effects from static abilities prevent or replace damage from sources with certain properties. For these effects, the prevention or replacement applies to sources that are permanents with that property and to any sources that aren’t in play that have that property.

419.9. Interaction of Replacement or Prevention Effects

419.9a If two or more replacement 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. Then the other effect applies if it is still appropriate. If one or more of the applicable replacement effects is a self-replacement effect (see rule 419.6d), that effect is applied before any other replacement effects. If two or more players have to make these choices at the same time, choices are made in APNAP order (see rule 103.4).

Example: Two permanents are in play. One is an enchantment that reads “If a card would be put into a graveyard, instead remove it from the game,” and the other is a creature that reads “If [this creature] would be put into a graveyard from play, instead shuffle it into its owner’s library.” The controller of the creature that would be destroyed decides which replacement to apply first; the other does nothing.

419.9b A replacement effect can become applicable to an event as the result of another replacement effect that modifies the event.

Example: One effect reads “For each 1 life you would gain, instead draw a card,” 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 his or her graveyard into his or her hand.

420.1. State-based effects are a special category that apply only to those conditions listed below. Abilities that watch for a specified game state are triggered abilities, not state-based effects. (See rule 404, “Triggered Abilities.”)

420.2. State-based effects are always active and are not controlled by any player.

420.3. Whenever a player would get priority (see rule 408, “Timing of Spells and Abilities”), the game checks for any of the listed conditions for state-based effects. All applicable effects resolve as a single event, then the check is repeated. Once no more state-based effects have been generated, triggered abilities go on the stack, and then the appropriate player gets priority. This check is also made during the cleanup step (see rule 314); if any of the listed conditions apply, the active player receives priority.

420.4. Unlike triggered abilities, state-based effects pay no attention to what happens during the resolution of a spell or ability.

Example: A player controls a creature with the ability “This creature’s power and toughness are each equal to the number of cards in your hand” and plays a spell whose effect is “Discard your hand, then draw seven cards.” The creature will temporarily have toughness 0 in the middle of the spell’s resolution but will be back up to toughness 7 when the spell finishes resolving. Thus the creature will survive when state-based effects are checked. In contrast, an ability that triggers when the player has no cards in hand goes on the stack after the spell resolves, because its trigger event happened during resolution.

420.5. The state-based effects are as follows:

420.5a A player with 0 or less life loses the game.

420.5b A creature with toughness 0 or less is put into its owner’s graveyard. Regeneration can’t replace this event.

420.5c A creature with lethal damage, but greater than 0 toughness, is destroyed. Lethal damage is an amount of damage greater than or equal to a creature’s toughness. Regeneration can replace this event.

420.5d An Aura attached to an illegal permanent or player, or not attached to a permanent or player, is put into its owner’s graveyard.

420.5e If two or more legendary permanents with the same name are in play, all are put into their owners’ graveyards. This is called the “legend rule.” If only one of those permanents is legendary, this rule doesn’t apply.

420.5f A token in a zone other than the in-play zone ceases to exist.

420.5g A player who attempted to draw a card from an empty library since the last time state-based effects were checked loses the game.

420.5h A player with ten or more poison counters loses the game.

420.5i If two or more permanents have the supertype world, all except the one that has been a permanent with the world supertype in play for the shortest amount of time are put into their owners’ graveyards. In the event of a tie for the shortest amount of time, all are put into their owners’ graveyards. This is called the “world rule.”

420.5j A copy of a spell in a zone other than the stack ceases to exist. A copy of a card in any zone other than the stack or the in-play zone ceases to exist.

420.5k An Equipment attached to an illegal permanent becomes unattached from that permanent but remains in play.

420.5m A non-Aura, non-Equipment permanent attached to another permanent becomes unattached from that permanent but remains in play.

420.5n If a permanent has both a +1/+1 counter and a -1/-1 counter on it, N +1/+1 and N -1/-1 counters are removed from it, where N is the smaller of the number of +1/+1 and -1/-1 counters on it.

421.1. Occasionally the game can get into a state in which a set of actions could be repeated forever. These rules (sometimes called the “infinity rules”) govern how to break such loops.

421.2. If the loop contains one or more optional actions and one player controls them all, that player chooses a number. The loop is treated as repeating that many times or until another player intervenes, whichever comes first.

421.3. If a loop contains optional actions controlled by two players and actions by both of those players are required to continue the loop, the first player (or the first involved player after the active player in turn order) chooses a number. The other player then has two choices. He or she can choose a lower number, in which case the loop continues that number of times plus whatever fraction is necessary for the active player to “have the last word.” Or he or she can agree to the number the first player chose, in which case the loop continues that number of times plus whatever fraction is necessary for the second player to “have the last word.” (Note that either fraction may be zero.) This sequence of choices is extended to all applicable players if there are more than two players involved.

Example: In a two-player game, one player controls a creature with the ability “{0}: [This creature] gains flying,” and another player controls a permanent with the ability “{0}: Target creature loses flying.” The “infinity rule” ensures that regardless of which player initiated the gain/lose flying ability, the nonactive player will always have the final choice and therefore be able to determine whether the creature has flying. (Note that this assumes that the first player attempted to give the creature flying at least once.)