The following document contains information originally provided by Stelios Kargotis.

The Interaction of Continuous Effects

Introduction

Layers or the Interaction of Continuous Effects is one of the most challenging areas for players and judges to learn and master. The main reason for this is that when spells or abilities, which generate multiple continuous effects come off the stack they do not always apply in the last on first off rule.
In fact the way that they interact is considered by some, counter intuitive which causes the majority of problems for players and judges.
Besides being counter intuitive, Layers like all things challenging in Magic have a bit of a bad reputation. Prior to the creation of layers, rulings which involved the fabled Humility and Opalescence would cause a lot of issues, this coupled with the first system of layers caused a lot of untold headaches and subsequently became an area that most wanted to avoid.
So to that end, this seminar will attempt to dispel the myths surrounding this topic and look at the Interaction of Continuous Effects in detail. To assist our learning in this subject there will be a number of examples to help you digest all that you need to know.

Types of effects

So before we look at the layers themselves we need to briefly look at the two types of effects that are generated in Magic and what generates them. According to the Comprehensive Rules there are two types of effects:

• 1. One-Shot Effects

A one shot effect does something just once and has no duration. Examples include dealing damage, destroying a permanent, putting a token onto the battlefield and moving an object from one zone to the other.

• 2. Continuous Effects

A Continuous effect modifies characteristics of objects, modifies control of objects or affects players or the rules of the game for a fixed or indefinite period. Examples include setting power and toughness on a creature, changing its colour, changing its controller and giving it abilities.
Continuous effects & One Shot effects are generated by a spell or an ability.

So now that we have covered the different types of effects its time to discuss how these effects interact. To do that we need to look at 4 main concepts: Layers, Timestamps, Dependency and CDA’s (Characteristic Defining Abilities).

1. The Layers

There are 7 main layers:

1) Copy
If the spell or the ability has the word Copy the effect it produces will sit in this layer.

2) Control
If a spell or an ability alters the control of a permanent then it will sit in this layer.

3) Text
If a spell or an ability alters the text of permanent then it will sit in this layer.

4) Type
If a spell or an ability alters the Super type, type or subtype of a permanent then it sits in this layer.

5) Colour
If a spell or an ability alters the Colour of a permanent then it sits in this layers.

6) Adding or Removing abilities
If a spell or an ability adds or removes an ability then it sits in this layer.

7) Power and Toughness
If a spell or an ability alters the Power and Toughness of a creature then it sits in this layer. However due to the different types of abilities that can alter the Power and Toughness of a creature, Layer 7 has and additional 5 sub layers. They are:

• 7a)CDA’s Example: The Power and Toughness of this permanent is equal to the amount of swamps in play.

• 7b) Setting Power & Toughness to a specific number or value. Example: Target artifact is now a 5/5 Creature.

• 7c) Effects that modify Power and Toughness but do not set to a specific value. Example: target creature gains +3/+3 or target creature gains -3/+3.

• 7d) Power and/or toughness changes from counters are applied here.

• 7e) Effects that switch a creatures power and toughness are applied in this layer.

2. Time Stamps

During a game of Magic it is common and possible to have multiple effects occurring in the same layer or sublayer. To that end, the mechanics of the game need to determine which order continuous effects are applied in and this is done using the timestamp system. An effect with an earlier timestamp is applied before an effect with a later timestamp. In other words the continuous effect with the newest time stamp will overwrite the effect with the older time stamp.
So when does a continuous effect gain its time stamp?
Well, the game has 7 rules which govern the “allocation” of timestamps to continuous effects, they are:

1) A Continuous effect generated by a static ability has the same timestamp as the object of the static ability is on, or the timestamp of the effect that created the ability, which ever is the later.
2) Continuous effect generated by the resolution of a spell or ability receives a timestamp at the time its created.
3) An objects timestamp is the time it entered into the zone its currently in, unless its an Aura, Equipment or Fortification that’s attached to another object or player, or its a face up plane card.
4) If an Aura, Equipment or Fortification becomes attached to a object or player then it receives a new timestamp at that time.
5) A face up plane card or scheme card receives a timestamp at the time its turned face up.
6) A face up vanguard card receives a timestamp at the beginning of the game.
7) If two or more objects would receive a timestamp simultaneously such as entering a zone simultaneously, or becoming attached simultaneously, the active player determines their timestamp order at that time.

3. Dependency

Dependency is a game concept which negates the timestamp system and for that reason does not occur very often. However it something we as Judges need to be aware of and understand. The best way of explaining dependency is looking at its most famous example Blood Moon and Urborg, Tomb of Yawgmoth.
Blood Moon‘s text says All none basic lands are Mountains. Urborg, Tomb of Yawgmoth states Each Land is a Swamp in addition to its other land types. So how do these effects interact?
So both these cards have abilities which alter Land Types and thus they both apply in Layer 4.
If Urborg is on the battlefield and Blood Moon comes onto the battlefield. Urborg becomes a Mountain. However if Blood Moon is on the battlefield and Urborg is played, Urborg is still a Mountain. This is due to the fact that Blood Moon’s text changes the text on Urborg but Urborg does not change the text or the existence of Blood Moons continuous effect.
One last proviso for dependency to occur is neither effect is from a Characteristic Defining Ability. If this is the case the effect is considered to be independent of the other effect.
In addition to the above rules governing dependency the following also applies:
“An effect which is dependent on one or more effects waits to apply until just after all of those effects would have been applied. If multiple dependent effects would apply simultaneously in this way they are applied in timestamp order relative to each other. If they would form a loop then this rule is ignored and they are applied in timestamp order.

4. Characteristic Defining Abilities (CDA)

Definition of a Characteristic:
Name, mana cost, colour, card type, subtype, supertype, expansion symbol, rules text, abilities, power and toughness, loyalty, hand modifier and life modifier. Any other information about an object is not a characteristic.

Definition of a CDA:

A CDA is a type of static ability which conveys information about an objects characteristics that would normally be found elsewhere on that object.

Example: Korlash, Heir to Blackblade has a CDA that says “The power and toughness of Korlash is equal to the amount of swamps in play”.

All CDA’s must adhere to the following rules:
1) It defines an objects colours, subtypes, power and/or toughness.
2) It is printed on the card it affects or it was granted to the token it affects by the effect that created the token, or it was acquired by the object it affects as the result of a copy effect or text changing effect.
3) It does not directly affect the characteristics of any other objects
4) It is not an ability which it grants to itself
5) It does not set the values of such characteristics only if certain conditions are met.
When applying continuous effects its worth noting that CDA’s are applied first in every layer and then all other continuous effects in timestamp order.

Questions for the Interaction of Continuous Effects

• Q1: Akon controls Honor of the Pure and a Steppe Lynx. He plays an Arid Mesa. In response to the Steppe Lynx trigger, Nelly plays Turn to Frog targeting the Lynx. Akon responds by sacrificing the Arid Mesa. Nelly responds by playing Twisted Image on the Lynx. Akon lets Twisted Image resolve and then plays Inspired Charge.
  What is the Power and Toughness of Steppe Lynx?
• Q2: Player 1 controls Magus of the Moon and Player 2 has Urborg, Tomb of Yawgmoth, Mystic Gate, Tundra and Taiga on the battlefield. Player 2 casts and resolves Humility.
  What can each land tap for?
• Q3: Player 1 controls Feral Hydra and Player 2 casts Snakeform .
  What happens next?
• Q4: Player 1 controls Eager Cadet, Mutavault and a face down 2/2 morph. Player 1 activates the Mutavault and declares all three as attackers. Player 2, during the declare blockers step casts Mirrorweave targetting the Mutavault.
  How much damage does Player 2 take?
• Q5: Player 1 controls Glory Seeker, which has a +1/+1 counter on it. Player 2 activates Merfolk Thaumaturgist‘s ability, targeting Glory Seeker. After Merfolk Thaumaturgist‘s ability resolves, Player 2 activates Serendib Sorcerer‘s ability, targeting Glory Seeker.
  What happens next?
• Q6: If one player has Necrotic Ooze in play, and another player has Yixlid Jailer, how do the abilities interact (assuming that there are creature cards in the graveyard that would normally have activated abilities if they were creatures in play)?
  What happens if another creature with an activated ability goes to the graveyard whilst both of these cards are in play?