The layers system
This page is current as of Comprehensive Rules October 2010. Please direct your feedback to: The Staff
With over eleven thousand cards and counting, Magic sports a great variety of effects. When these effects are continuous, they interact with one another in ways that may not always be intuitive or easy to understand. If you're a judge or have been thinking to become one, you probably don't need to be reminded of this card:
Mark Rosewater recounts that, after designing Humility, he was really satisfied of his creation, that he deemed simple and easy. And it really is, by itself. The pain begins when Humility interacts with other cards.
For years, rulings were handled on a case-by-case basis by Stephen D'Angelo, a rules guru that wasn't even affiliated with Wizards of the Coast[1]. When Sixth Edition was released, the rules faced a major reworking, with the creation of that fine document that is Comprehensive Rules; this update introduced a system to handle the interaction of continuous effects that - albeit with several tweaks - is still in use today, and tries to held results that are, in this order:
- Univocally determined
- Similar to what a player would intuitively guess
- Akin to the "pre-revisionist" rulings
Contents
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Overview
This system classifies all possible effects in seven categories, known as layers, and specifies the order in which these categories should be evaluated. We'll discuss in detail these categories and see what goes in each, since properly dividing effects among them is paramount for correct interpretation of difficult board states.
Other rules specify the relative order of effects within each layer. Generally speaking, effects that provide values usually printed on cards are applied first, then other effects follow in the order they were generated - with an important exception in case they interfere with each other.
The target of this very long set of rules is to order all the continuous effects that could coexist. After doing this, the actual calculation of the results they yield is trivial.
The layers
Each continuous effect belongs to exactly one of the following layers (and, if applicable, sub-layer). [CR 613.1] If an effect does more than one thing, it has to be split and the single parts applied in the appropriate layers. [CR 613.5]
- Copy effects
- Control-changing effects
- Text-changing effects
- Type-changing effects[2]
- Color-changing effects
- Effects that add or remove abilities
- Effects that alter power and/or toughness
- 7a. Effects from characteristic-defining abilities
- 7b. Effects that set power and/or toughness to a specific value
- 7c. Effects that increase or decrease power and/or toughness
- 7d. Effects from counters
- 7e. Effects that switch power and toughness
Copy effects
Copy effects are easy to spot: they always use the word copy, and only these effects use this term. [CR 706.1] Copy effects have very specific rules on what their result will be; at this time, it's important to note that some effects copy an object with some exceptions, whereas others copy an object and then further modify the copy. The two should not be confused: exceptions to a copy effect are part of the copy effect itself, and are applied with it in the layer 1; further modification go in the appropriate layer. Effects of the first kind can be recognized because they use the word except. [CR 706.8b]
| Example. Quicksilver Gargantuan copies a creature, except it's still 7/7. This is a copy effect with an exception, so it's all applied in layer 1. If Clone enters the battlefield as a copy of a Quicksilver Gargantuan that is copying something else, Clone will be 7/7.
Kiki-Jiki, Mirror Breaker, on the other hand, creates a copy of a creature and then gives the token haste. If a Clone becomes a copy of the token, it will not have haste. |
Kiki-Jiki, Mirror Breaker
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Control-changing effects
These effects change who controls a given permanent. There's not much to say, except that effects that put onto the battlefield stuff under a player's control are not control-changing effects.
Text-changing effects
These effects alter the text of a card, defined as its rules text plus its type line. These effects always use the words change the text, and never affect names or mana symbols. [CR 612.1] Note that abilities granted to permanents are not present in their text box, so can't be affected by text-changing effects. [CR 612.3]
There is only one exception to this rule, the incredibly quirky Volrath's Shapeshifter, that has a special text-changing effect that alters not only its rules text and type line, but also name, mana cost, expansion symbol, power, and toughness. [CR 612.5]
Example. A Circle of Protection: Black on the battlefield is targeted by Mind Bend. Upon resolution, the devious blue mage changes "black" with "green", which allows him to prevent damage from the menacing Force of Nature he's facing. Targeting the mighty Elemental with Mind Bend has no effect, since the  cost it requires as an upkeep is not affected.
If a Pithing Needle enters the battlefield and CoP: Black is chosen, the mind-bent enchantment can't be activated, since its name was not changed. |
Mind Bend |
Type-changing effects
All effects that change or grant additional types, subtypes or supertypes to permanents fall in this category. These effects are quite common: several cards alter supertypes (Leyline of Singularity), types (Nature's Revolt) or subtypes (Dralnu's Crusade).
Color-changing effects
Guess what? These effects change the color of the affected permanent. Remember that portions of other effects that change colors fall here, and that if you have to choose a color, you must choose from among white, blue, black, red, green and purple. You can't choose stuff like "colorless", "artifact", "Elf", "Tex", and other such frivolities. [CR 105.1],[CR 105.4]
Effects that add or remove abilities
Effects that say that a permanent gains an ability, has an ability, or use the word with - as in "becomes a creature with flying" - are adding abilities to that permanent. Effects that say that a permanent loses an ability or make it into a permanent with no abilities are removing abilities. [CR 112.10]
Note that if a permanent has multiple instances of the same keyword ability (redundant or not) and an effect removes that keyword ability, it removes all instances.
Effects that alter power and/or toughness
Since creature combat is the focus of the game, there's a great number of effects that grow or shrink creatures. For this reason, effects that fall inside this layer are not ordered as in the other layers. Instead, they are distributed among five sub-layers; within each sub-layer, the aforementioned rules for ordering apply.
Effects from characteristic-defining abilities
Characteristic-defining abilities are a class of static abilities that's defined very strictly. Those abilities define values that are usually flat-out printed on the card, usually in order to have them vary during the course of game play. [CR 604.3]
A characteristic-defining ability is an ability that respects all the following requirements [CR 604.3a]:
- It defines a characteristic, such as color, subtype, power or toughness.
- It's intrinsic to the permanent. This means that it's printed on the actual cardboard, granted to a token by the very same effect that creates it, or gained by means of a copy or text-changing effect. The abilities granted by any other mean are not intrinsic, not even when an object grants an ability to itself.
- It only affects the characteristic of the object it's on.
- It's not conditional. Abilities that work only when some condition is met are not welcome here.
Characteristic-defining abilities have an important property: they work in all zones, not only from the battlefield. [CR 604.3]
Effects that set power and/or toughness to a specific value
These effects simply state that power and/or toughness become a certain number. These effects are generated by abilities from non-creature permanents that "animate" and become creatures (Jade Statue, Mutavault), by static abilities (Humility, Gigantiform), or by resolving objects (Sorceress Queen, Humble). We don't care about the source: if it sets the values, it goes here.
Effects that increase or decrease power and/or toughness
This layer includes effects that raise or lower power and/or toughness, such as Giant Growth, Nameless Inversion, Crusade, Mutilate, Looming Shade and countless others.
Effects from counters
Counters increase or decrease power and toughness, so there's no reason to segregate them here. I guess we'll just have to deal with it.
Effects that switch power and toughness
These effects always use the word switch.
| Example. Windreaver is on the battlefield with a +1/+1 counter on it. Its controller attacks with it, activates its third activated ability twice, casts Giant Growth on it and then activates its fourth activated ability, hoping to deal massive amount of damage. After all this stuff resolved, the defending player casts Humble on the not-so-humble Windreaver. How does it look like now?
We always start by distributing the effects in the appropriate layers, then we apply them on the original object. In this case, they all modify power and toughness, so they all live in layer 7. The counter goes in 7d, the +0/+1 activations in 7c, Giant Growth in 7c as well, the switch in 7e and Humble in 7b. So:
The Windreaver ends up as a massive 7/4 - probably not what the defending player was hoping to obtain! |
Humble
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Effects that span several layers
Sometimes, a single effect can be divided into smaller chunks, each of which would fall into a different layer. In this case, we treat it as though each portion was a stand-alone continuous effect, with a very important difference: once an effect has started applying, all of its parts will apply in the appropriate layer, even if the ability that generated it is removed during the way. [CR 613.5]
Example. Natural Emergence has a static ability that generates a complex effect, that can be divided as follows:
Now, let's suppose Humility and Opalescence are on the battlefield. This notorious combo will make Natural Emergence a creature, and Humility will strip away its abilities. What do the animated lands look like?
Since the effect from Natural Emergence started applying in layer 4, before being removed by Humility in layer 6, all parts of it will apply. Even though in layer 7 its source ability is long gone, it will still apply. The actual results of this derelict situation depends on the order we apply effects in the same layer, which is the matter of the next paragraph. |
Natural Emergence |
Order within layers
Layers are useful to sort effects of different nature. However, similar effects fall into the same layer, and we need to establish a way to order those as well. In a pinch, we apply the following rules:
- Effects from characteristic-defining abilities are always applied first
- Then, dependent effects are ordered so that each dependent effect is applied after all effects it depends on
- Then, independent effects are applied in timestamp order [CR 613.2]
Effects from characteristic-defining abilities
Characteristic-defining abilities are a class of static abilities that's defined very strictly. Those abilities define values that are usually flat-out printed on the card, usually in order to have them vary during the course of game play.
A characteristic-defining ability is an ability that respects all the following requirements:
- It defines a characteristic, such as color, subtype, power or toughness.
- It's intrinsic to the permanent. This means that it's printed on the actual cardboard, granted to a token by the very same effect that creates it, or gained by means of a copy or text-changing effect. The abilities granted by any other mean are not intrinsic, not even when an object grants an ability to itself.
- It only affects the characteristic of the object it's on.
- It's not conditional. Abilities that work only when some condition is met are not welcome here.
Characteristic-defining abilities have an important property: they work in all zones, not only from the battlefield.
Dependent effects
Let's suppose you have Crusade on the battlefield; then, your devious opponent casts Celestial Dawn. Your opponent's creatures are now white, but do they receive the +1/+1 bonus from your Crusade? [3]After all, they weren't part of the crusade in the first place...
Sometimes, an effect can influence an other, changing:
- the existence of the first effect
- what it applies to
- what it does to any of the things it applies to
If both effects apply in the same layer, and neither is a characteristic-defining ability, the second effect depends on the first. [CR 613.7a]
Sometimes, you may have effect A that depends on effect B, B that depends on C, and C that depends on A. In this case, we have a dependency loop, and we apply the Ostrich algorithm[4]: we outright ignore the loop, and treat these dependency relationships as though they didn't exist. [CR 613.7b]
| Example. Humility erases the ability on Lord of Atlantis, so the effect that gives Islandwalk to Merfolk depends on the effect of Humility that removes abilities. On the other hand, note that the effect that gives Merfolks +1/+1 does not depend from the effect from Humility that makes critters 1/1, since they apply in different sub-layers.
Conversion turns Mountains into Plains. Then an Island is targeted by Mystic Compass, and the artifact's controller chooses to turn it into a Mountain. Conversion's effect will start applying to it, so it depends on Mystic Compass'. |
Humility
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We now know to tell dependent effects.[5] We can now use this to order depending effects, and this is how we do it: when an effect depends on one or more other effects, it is always applied after all the effects it depends on.
Timestamp order
When there is no dependency among effects, we simply apply them in the order they were created. This is usually very simple, but we may need a formal definition of the timestamp each effect receives. The simplest version of the rule can be laid out as follows:
- The timestamp for continuous effects generated by resolving spells and abilities is the time the source resolved. [CR 613.6b]
- The timestamp for continuous effects generated by static abilities is the time the permanent with the ability entered the zone it's currently in. [CR 613.6a]
| Example. A land is both enchanted by Spreading Seas and targeted by Tideshaper Mystic's ability, choosing Plains. Both effects apply in layer 4, and neither is a dependent effect, so they are ordered in timestamp order. The timestamp of the Spreading Seas' effect is the time Spreading Seas entered the battlefield; the timestamp of the effect from the Tideshaper Mystic's ability is the time the ability resolved.
So, if the land is already enchanted when the Merfolk's ability resolves, it will be a Plains; if the ability is activated in response to the Aura, it will be an Island. Note that the fact that one effect has a duration whereas the other lasts indefinitely is irrelevant. |
Spreading Seas |
There's a couple of juicy side rules regarding effects generated by static abilities:
- If a permanent gains a static ability, the timestamp of the effect generated by that ability will be either the time the permanent entered the battlefield or the time it gained the ability, whichever is later. [CR 613.6a]
- Auras and Equipments[6] receive a new timestamp when they are moved to a new permanent or player. [CR 613.6d]
| Example. The young and eager Kalle has casted an Argothian Wurm and a Shivan Dragon, but the devious Dave has casted a Mind Control on Kalle's Shivan Dragon. Kalle takes back his monster casting Insurrection, and swings with both creatures: Insurrection has a later timestamp than Mind Control, and thus overrides it.
During combat, Dave casts Aura Finesse on his Mind Control, and attachs it to Argothian Wurm. This resets the timestamp of Mind Control, and makes it earlier than the timestamp of Insurrection, so he gains control of the Wurm, which is removed from combat. Note that he could legally choose the Shivan Dragon as a target for the Aura Finesse, but since in this case the Mind Control wouldn't have actually moved, its timestamp would have stayed the same. |
Insurrection |
Paralipomena
(Would you believe it's a real word? Me neither.)
This set of rules should be applied only to continuous effects that modify characteristics or control of objects. These are the great majority of the effects we usually find on cards, but a brief summary of other kind of effects is in order:
- Some effects affect players rather objects, for example granting them protection from something. [CR 613.9] These effects are applied after the whole layer madness has been handled, according to timestamp and dependency rules. They sort of live in an imaginary eighth layer.
- Some effects modify game rules: for example, they might change the maximum hand size for a player, state that a permanent is indestructible or that creatures are unblockable. [CR 613.10] These are applied after object characteristics have been calculated, according to timestamp and dependency rules.
- Some effect affect the cost of spell and abilities. These effects have their own set of rules.
- Some effects are replacement effects, and we talk about them somewhere else.
Footnotes
↑ I think.
↑ For very large values of type: we include here effects that change an object's card type, subtype, and/or supertype. [CR 613.1d]
↑ Note that this is not an example of dependent effects, since they don't apply in the same layer.
↑ Which is a real technique used in computer science!
↑ Have a look at this message on MTGRules-L to understand what it takes to exhaustively tackle the problem.
↑ And Fortifications, too, you nitpicking completist!
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