Prevention effect

A prevention effect is a continuous effect that acts as a shield against damage. Most are specific and limited as to which damage interactions would be prevented, such as "prevent all damage that would be dealt to you this turn by a source of your choice". Prevention effects behave similarly to replacement effects: they replace the damage part of an event with "nothing" or with a reduced amount of damage.

Description

Prevention effects can come from one-time spells and effects, or from static abilities. They are usually limited in several ways, such as by which recipients of damage are protected (e.g. "to you", "to [this creature]", "to a creature you control"), which sources of damage the prevention works against, a duration or specific event the effect applies (e.g. "this turn" or "the next time damage would be dealt"), and how much damage in any damaging event is prevented (e.g. "the next 3 damage"). Some effects say damage "can't be prevented", which may apply to a single damage event or to all damage within a specified duration. A few cards have abilities that trigger when damage is prevented.

Damage prevention prevents the direct results of damage, which are usually accumulation of damage that may be lethal damage, loss of life, or loyalty counters. It also includes those from Infect, Wither, Toxic, Lifelink, and can prevent effects that would've replaced the damage with something else. It stops or reduces indirect consequences such as abilities that trigger from damage being dealt as well. If damage is reduced to 0 by prevention, those abilities will not trigger at all.

Some effects cause loss of life without "damage". These are unaffected by damage prevention.

Related mechanics

Damage prevention is closely related to replacement effects and follows most of the same rules. If multiple prevention or replacement effects would apply to the same player or permanent, that player or controller chooses the order they're applied; sometimes applying one effect first may make others inapplicable. However, replacement effects that replace damage with something else without using the word "prevent" aren't prevention effects, and ignore "can't be prevented" clauses.

Redirection effects are similar but distinct from prevention: damage that would've been dealt to a permanent or player is dealt somewhere else instead. These are usually replacement effects and do not use the word "prevent", so "can't be prevented" effects don't apply. Prevention effects can behave almost like redirection, using an "if damage is prevented this way" triggered ability to deal the prevented damage somewhere else (e.g. Phyrexian Vindicator).

Shield counter rules define a static prevention effect combined with indestructibility for any permanent the counter is on, but the counter is removed as the prevention happens. It's still removed even if it fails to prevent damage due to "can't be prevented" effects.

All prevention effects pertain to damage itself rather than related game events or conditions. For instance, countering a spell, removing a creature from combat, or a static ability that states a certain kind of event "can't happen" are not prevention effects. Preventing damage from a spell, ability, or combat doesn't counter the spell, affect the source of the ability, or prevent a creature from attacking or blocking.

History

In the early history of the game, damage prevention was somewhat common and was considered a special category of effect with its own place in the timing rules, together with damage redirection (which is now a subtype of replacement effect) and Regeneration. Creatures that tapped to prevent damage were perhaps the most common, such as the classic Samite Healer. R&D has stated it has scaled back on doing damage prevention, because it adds a lot of board complexity and slows the game down. It's primary in white. The last partial prevention effect was printed in 2021 (Valkmira, Protector's Shield (Kaldheim)) and there have been no others since 2018 in Dominaria.

The Fog style of prevention of all combat damage, nicknamed after the Alpha card which began the trend, has continued to appear on new or reprinted cards for over 25 years now, for instance Root Snare in Core Set 2019. Gaseous form is a similar style of two-way preventing effect that has continued to see print. Self-affecting prevention effects are often used by planeswalkers who can become creatures, such as Gideon Jura. A more modern example, a specialized card with built-in limitations, is Nine Lives.

Variations using counters

Permanents with damage prevention can be kept balanced with counters that must be removed each time damage is prevented, for example Spore Flower, Fylgja, or Defender en-Vec. These may have additional abilities to replenish the counters. Shield counters have built-in rules prevent damage and destruction while removing themselves automatically.

A specific variation of this is for low-toughness creatures to have counters to prevent damage to themselves, as with Rasputin Dreamweaver. This is especially common specifically with 0/0 creatures that come into play with +1/+1 counters which are then removed to prevent damage. This essentially turns "taking damage" into "removal of counters"; unlike damage, this affects both power and toughness and is permanent. This ability first appeared on Rock Hydra in Alpha, and it is still associated with Hydras, although not limited to them. As with other permanents, there is often a way to replenish counters. Thus, it's somewhat of a precursor to the planeswalker loyalty system.

Depending on the ability phrasing of a creature - like Protean Hydra or Unbreathing Horde - it may become "invulnerable" to damage if its toughness is modified to be non-zero without the use of counters, such as with an enchantment. This allows it to continue preventing all damage, but not losing toughness because it has no further counters to remove. Undergrowth Champion from Battle for Zendikar was the first creature printed with a specific clause to prevent this situation, although Rock Hydra's own revised oracle text uses the same phrasing.

One variant is the "Phantom ability", named for a series of creatures in the Judgement set named "Phantom [creature]", such as Phantom Nishoba. These creatures prevent all damage to themselves at the cost of a single counter per damaging event.

A rarer variant is the inversion of the role of counters and base power/toughness by putting -1/-1 counters onto a creature with high statistics, rather removing counters from one with low toughness, as with Phyrexian Hydra and Lichenthrope. This is rare not from complexity but from the lack of design space for -1/-1 counters. One other variant reverses the effect entirely, by gaining +1/+1 counters with damage taken, as with Phytohydra and Ironscale Hydra, which naturally causes the creature's stats to increase rather than trend toward 0 toughness.

Rules

From the glossary of the Comprehensive Rules (June 7, 2024—Modern Horizons 3)

Prevention Effect

A kind of continuous effect that watches for a damage event that would happen and completely or partially prevents the damage that would be dealt. See rule 615, “Prevention Effects.”

From the Comprehensive Rules (June 7, 2024—Modern Horizons 3)

• 615. Prevention Effects
  • 615.1. Some continuous effects are prevention effects. Like replacement effects (see rule 614), prevention effects apply continuously as events happen—they aren’t locked in ahead of time. Such effects watch for a damage event that would happen and completely or partially prevent the damage that would be dealt. They act like “shields” around whatever they’re affecting.
    • 615.1a Effects that use the word “prevent” are prevention effects. Prevention effects use “prevent” to indicate what damage will not be dealt.
  • 615.2. Many prevention effects apply to damage from a source. See rule 609.7.
  • 615.3. There are no special restrictions on casting a spell or activating an ability that generates a prevention effect. Such effects last until they’re used up or their duration has expired.
  • 615.4. Prevention effects must exist before the appropriate damage event occurs—they can’t “go back in time” and change something that’s already happened. Spells or abilities that generate these effects are often cast or activated in response to whatever would produce the event and thus resolve before that event would occur.

    Example: A player can activate an ability that prevents damage in response to a spell that would deal damage. Once the spell resolves, though, it’s too late to prevent the damage.

  • 615.5. Some prevention effects also include an additional effect, which may refer to the amount of damage that was prevented. The prevention takes place at the time the original event would have happened; the rest of the effect takes place immediately afterward.
  • 615.6. If damage that would be dealt is prevented, it never happens. A modified event may occur instead, which may in turn trigger abilities. Note that the modified event may contain instructions that can’t be carried out, in which case the impossible instruction is simply ignored.
  • 615.7. Some prevention effects generated by the resolution of a spell or ability refer to a specific amount of damage—for example, “Prevent the next 3 damage that would be dealt to any target this turn.” These work like shields. Each 1 damage that would be dealt to the “shielded” permanent or player is prevented. Preventing 1 damage reduces the remaining shield by 1. If damage would be dealt to the shielded permanent or player by two or more applicable sources at the same time, the player or the controller of the permanent chooses which damage the shield prevents. Once the shield has been reduced to 0, any remaining damage is dealt normally. Such effects count only the amount of damage; the number of events or sources dealing it doesn’t matter.
  • 615.8. Some prevention effects generated by the resolution of a spell or ability refer to the next time a specific source would deal damage. These effects prevent the next instance of damage from that source, regardless of how much damage that is. Once an instance of damage from that source has been prevented, any subsequent instances of damage that would be dealt by that source are dealt normally.
  • 615.9. Some effects generated by the resolution of a spell or ability prevent damage from a source of a player’s choice with certain properties. When the source would deal damage, the shield rechecks the source’s properties. If the properties no longer match, the damage isn’t prevented or replaced and the shield isn’t used up. See rule 609.7b.
  • 615.10. Some prevention effects generated by static abilities refer to a specific amount of damage—for example, “If a source would deal damage to you, prevent 1 of that damage.” Such an effect prevents only the indicated amount of damage in any applicable damage event at any given time. It will apply separately to damage from other applicable events that would happen at the same time, or at a different time.

    Example: Daunting Defender says “If a source would deal damage to a Cleric creature you control, prevent 1 of that damage.” Pyroclasm says “Pyroclasm deals 2 damage to each creature.” Pyroclasm will deal 1 damage to each Cleric creature controlled by Daunting Defender’s controller. It will deal 2 damage to each other creature.

  • 615.11. Some prevention effects prevent the next N damage that would be dealt to each of a number of untargeted creatures. Such an effect creates a prevention shield for each applicable creature when the spell or ability that generates that effect resolves.

    Example: Wojek Apothecary has an ability that says “{T}: Prevent the next 1 damage that would be dealt to target creature and each other creature that shares a color with it this turn.” When the ability resolves, it gives the target creature and each other creature on the battlefield that shares a color with it at that time a shield preventing the next 1 damage that would be dealt to it. Changing creatures’ colors after the ability resolves doesn’t add or remove shields, and creatures that enter the battlefield later in the turn don’t get the shield.

  • 615.12. Some effects state that damage “can’t be prevented.” If unpreventable damage would be dealt, any applicable prevention effects are still applied to it. Those effects won’t prevent any damage, but any additional effects they have will take place. Existing damage prevention shields won’t be reduced by damage that can’t be prevented.
    • 615.12a A prevention effect is applied to any particular unpreventable damage event just once. It won’t invoke itself repeatedly trying to prevent that damage.
  • 615.13. Some triggered abilities trigger when damage that would be dealt is prevented. Such an ability triggers each time a prevention effect is applied to one or more simultaneous damage events and prevents some or all of that damage.
• 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 If any of the replacement and/or prevention effects would cause a card to enter the battlefield with its back face up, one of them must be chosen (See rule 701.28, “Transform,” and rule 701.50, “Convert.”). If not, proceed to 616.1e.
    • 616.1e Any of the applicable replacement and/or prevention effects may be chosen.
    • 616.1f 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.

    • 616.1g While following the steps in 616.1a–f, 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.

From the glossary of the Comprehensive Rules (June 7, 2024—Modern Horizons 3)

Prevent

A word used by prevention effects to indicate what damage will not be dealt. See rule 615, “Prevention Effects.”