Information about this series

I have been planning on doing several articles on concepts of the game that are not understood by every player, mainly because they do not pop up as frequently.
I realize plenty of articles already exist, but players will not go looking for them. I plan to make these articles not too technical, but instead focus on realistic scenarios where the topic is relevant. I realize my definition of "not too technical" may be different from other people .

Topics

• State Based Actions
  
• Casting a Spell
  
• Simplified Layers
  
• How to become a judge
  
• ...
  

If you have any topic you want to have covered, let me know. These are the ones I could come up with in a limited amount of time.
I will try to write out topic every two weeks, but I cannot guarantee anything.

Resources

If you want to know more about a topic, or have questions, feel free to leave them as a reply or personal message.
In case I cannot reply, or you need an immediate answer, you can always ask your question here: http://chat.magicjudges.org/mtgrules/
This is a chat where judges are present (or more technically, a web interface to the irc channel #mtgjudge on irc.efnet.org). Just ask your question politely, and you should get an answer fairly quickly.

Player Names

Whenever an example is given, a player will have a name starting with either an N or an A. A name starting with A means that this player is the active player (AP), or the player whose turn it is. A player name starting with N means this player is the non-active player (NAP).

State Based Actions

The very first article will be about State Based Actions, or SBA in short. SBAs are constantly present, but players don't always know it.
SBAs are a list of actions the game checks whenever a player would get priority, and they do not use the stack. In other words, they are checked before a player can cast a spell or activate an ability. They are not checked while a spell or ability is resolving.

What are they?

SBAs are the little elves of the game, ensuring that everything remains clean, that things that should be dead actually die, and that players that should lose the game actually lose it.
The list of SBAs is the following, copied from the rules. We will discuss every one of them in detail, so don't be scared.

• If a player has 0 or less life, he or she loses the game.
  
• If a player attempted to draw a card from a library with no cards in it since the last time state-based actions were checked, he or she loses the game.
  
• If a player has ten or more poison counters, he or she loses the game.
  
• If a token is phased out, or is in a zone other than the battlefield, it ceases to exist.
  
• If a copy of a spell is in a zone other than the stack, it ceases to exist. If a copy of a card is in any zone other than the stack or the battlefield, it ceases to exist.
  
• If a creature has toughness 0 or less, it’s put into its owner’s graveyard. Regeneration can’t replace this event.
  
• If a creature has toughness greater than 0, and the total damage marked on it is greater than or equal to its toughness, that creature has been dealt lethal damage and is destroyed. Regeneration can replace this event.
  
• If a creature has toughness greater than 0, and it’s been dealt damage by a source with deathtouch since the last time state-based actions were checked, that creature is destroyed. Regeneration can replace this event.
  
• If a planeswalker has loyalty 0, it’s put into its owner’s graveyard.
  
• If a player controls two or more planeswalkers that share a planeswalker type, that player chooses one of them, and the rest are put into their owners’ graveyards. This is called the “planeswalker uniqueness rule.”
  
• If a player controls two or more legendary permanents with the same name, that player chooses one of them, and the rest are put into their owners’ graveyards. This is called the “legend rule.”
  
• If two or more permanents have the supertype world, all except the one that has had the world supertype 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.”
  
• If an Aura is attached to an illegal object or player, or is not attached to an object or player, that Aura is put into its owner’s graveyard.
  
• If an Equipment or Fortification is attached to an illegal permanent, it becomes unattached from that permanent. It remains on the battlefield.
  
• If a creature is attached to an object or player, it becomes unattached and remains on the battlefield. Similarly, if a permanent that’s neither an Aura, an Equipment, nor a Fortification is attached to an object or player, it becomes unattached and remains on the battlefield.
  
• 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.
  
• If a permanent with an ability that says it can’t have more than N counters of a certain kind on it has more than N counters of that kind on it, all but N of those counters are removed from it.
  

Well, thats quite a list. Let's break these down one by one:

• If a player has 0 or less life, he or she loses the game.
  

This one looks pretty straightforward. You lose the game when you have 0 or less life. Note that during the resolution of a spell you can go down to -1000, and as long as you have more than 0 life when the spell finishes resolving you are still alive and kicking.

Example
Albert and Nestor are both at 3 life. Albert casts a Lightning Bolt, targetting Nestor. Nestor responds by casting a lightning bolt himself, targetting Albert.
Nestor his copy resolves first, hereby reducing Albert his life total to 0. Before any of the two players would get priority, the game checks for SBAs and sees Albert is quite dead. His spells are removed from the stack, and Nestor wins the game.

• If a player attempted to draw a card from a library with no cards in it since the last time state-based actions were checked, he or she loses the game.
  

Whenever you try to draw a card from an empty library, you will lose the game. It does not matter if, after your spell resolved, your library contains cards again. This is death due to "milling".

Example
Albert has 1 card in his library. He casts Brainstorm, draws 1 card, fails to draw 2 more cards, and puts back 2 cards from his hand.
He will still lose the game, even though his library now contains 2 cards. This is why the SBA contains the part "since the last time state-based actions were checked", which may look a bit weird at first.

• If a player has ten or more poison counters, he or she loses the game.
  

Not much to say about this one, it is the same as the SBA for having 0 or less life, except for poison counters.

• If a token is phased out, or is in a zone other than the battlefield, it ceases to exist.
  

Phasing, one of the many abilities Wizards should not have made. For those who were not around when phasing existed (I wasn't), phasing made permanents 'phase in' and 'phase out' every turn. When a permanent is phased out, it does not exist according to the game (even though it does not go to a special zone). Phasing in does not trigger ETB triggers. Whenever a token phases out, it ceases to exist.

Example
There is only one relevant interaction in legacy, and that is the one between Sapphire Charm and Batterskull.
When a player targets the germ token, it will phase out and take the batterskull with it. The token will cease to exist, and not phase in again. As batterskull never phased out directly, it will not phase in. According to the game, it no longer exists, not even in exile, and cannot be retrieved.

• If a copy of a spell is in a zone other than the stack, it ceases to exist. If a copy of a card is in any zone other than the stack or the battlefield, it ceases to exist.
  

Copies of a spell can only exist on the stack. It does not make sense to have a copy of a spell in your GY, nor in your hand. The same with copies of cards, as they are not cards at all.

Example
The storm mechanic creates copies of cards, for example casting Empty the Warrens. Whenever a spell finishes resolving, it is put into the GY. The copy hits the GY, and then ceases to exist. Casting Remand on one of these copies will make the copy disappear in your hand once remand has resolved.

• If a creature has toughness 0 or less, it’s put into its owner’s graveyard. Regeneration can’t replace this event.
  

A creature with toughness 0 or less is put into its owner's graveyard. It is not destroyed, thus regeneration can't replace this event, nor can indestructibility save it.

Example
Albert controls a Darksteel Juggernaut and 1 other artifact.
Noah casts Grasp of Darkness, giving the juggernaut a toughness of -2. The juggernaut will be put into the GY nonetheless, even though it is indestructible.

• If a creature has toughness greater than 0, and the total damage marked on it is greater than or equal to its toughness, that creature has been dealt lethal damage and is destroyed. Regeneration can replace this event.
  

If a creature has more damage marked on it larger or equal to its toughness, it is destroyed. Seems fairly straightforward.

Example
The only tricky interaction are creatures whose toughness change throughout the game. In modern, the most common one is Tarmogoyf.
Albert controls a goyf, and he has a land and creature in his GY, making it a 2/3. Noah has an empty GY. Noah casts Lightning Bolt, targetting Goyf. Lightning bolt resolves, marks 3 damage on Goyf and is put into the graveyard. The game checks its SBAs, and sees a 3/4 goyf with 3 damage marked on it. Goyf continues its happy life.

• If a creature has toughness greater than 0, and it’s been dealt damage by a source with deathtouch since the last time state-based actions were checked, that creature is destroyed. Regeneration can replace this event.
  

If a creature is dealt damage by a source with deathtouch, that creature is destroyed, no matter its toughness. There is nothing tricky about this.

• If a planeswalker has loyalty 0, it’s put into its owner’s graveyard.
  

Once again, nothing tricky. Note that activating a minus ability on a PW, giving him a loyalty of 0, will put him in the GY before that ability resolves.

Example
Albert contains Jace, the Living Guildpact with 8 loyalty. He activates Jace's ultimate. Jace is put into the GY before that ability resolves.
Jace is thus shuffled back into the library.

• If a player controls two or more planeswalkers that share a planeswalker type, that player chooses one of them, and the rest are put into their owners’ graveyards. This is called the “planeswalker uniqueness rule.”
  
• If a player controls two or more legendary permanents with the same name, that player chooses one of them, and the rest are put into their owners’ graveyards. This is called the “legend rule.”
  

These two rules are intuitively the same for players: when you control multiple copies of the same legend, you need to select one of them and put the rest in the GY.
Note that Mirror Gallery does not remove the planeswalker uniqueness rule.

• If two or more permanents have the supertype world, all except the one that has had the world supertype 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.”
  

This does not happen in a magic game, so don't worry about it.

• If an Aura is attached to an illegal object or player, or is not attached to an object or player, that Aura is put into its owner’s graveyard.
  
• If an Equipment or Fortification is attached to an illegal permanent, it becomes unattached from that permanent. It remains on the battlefield.
  

Anything that is attached or equiped to something it should not be equiping is removed from it. The only difference between auras and equipments are that auras are put into the GY.

Example
Andy controls a grizzly bears, enchanted with Divine Favor and Daybreak Coronet.
Nelly casts Naturalize, targetting Divine Favor. Naturalize resolves, putting Divine Favor into the GY. When SBAs are checked, the game notices that Daybreak Coronet is enchanting something it cannot enchant, and thus it is placed into the GY.

• If a creature is attached to an object or player, it becomes unattached and remains on the battlefield. Similarly, if a permanent that’s neither an Aura, an Equipment, nor a Fortification is attached to an object or player, it becomes unattached and remains on the battlefield.
  

An animated equipment cannot be attached to anything. The game does not like it when creatures start swinging around other creatures, or things that are not designed to be swung around.

• 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.
  
• If a permanent with an ability that says it can’t have more than N counters of a certain kind on it has more than N counters of that kind on it, all but N of those counters are removed from it.
  

The game likes to keep the game state as simple as possible, thus it removes counters that cancel eachother. Obviously, magic used to have +2/+1 counters, -0/-1 counters etc.
SBAs do not clean these up, thus a creature can have a -0/-1 and a +0/+1 counter on it. I think the only played cards that have weird counters are Wall of Roots and Contagion.

When are they checked?

This little excerpt comes from the official rules. Once again, we'll break it down, so don't worry too much about it:

Whenever a player would get priority, the game checks for any of the listed conditions for state-based actions, then performs all applicable state-based actions simultaneously as a single event. If any state-based actions are performed as a result of a check, the check is repeated; otherwise all triggered abilities that are waiting to be put on the stack are put on the stack, then the check is repeated. Once no more state-based actions have been performed as the result of a check and no triggered abilities are waiting to be put on the stack, the appropriate player gets priority. This process also occurs during the cleanup step (see rule 514), except that if no state-based actions are performed as the result of the step's first check and no triggered abilities are waiting to be put on the stack, then no player gets priority and the step ends.

So let's see:

• Whenever a player would get priority
  

This is everytime a player would be able to play a spell or activate an ability. The SBAs are checked before that, meaning you cannot activate your Llanowar Elves after combat damage has been dealt and your elves would be destroyed.

• the game checks for any of the listed conditions for state-based actions, then performs all applicable state-based actions simultaneously as a single event
  

So, SBAs are all applied at once, thus players do not get to order these. This means that if both players were to die at the same moment, the game is a draw and not that some player wins and another one loses (depending on the ordering).

• If any state-based actions are performed as a result of a check, the check is repeated
  

Imagine a board state with Blood Artist, Ashenmoor Liege and Accursed Spirit. A player casts Pyroclasm.
Pyroclasm resolves, and SBAs are checked. The game notices a 1/2 Blood Artist (due to Liege) with 2 damage marked on it, a 4/1 Liege with 2 damage marked on it  and a 4/3 Spirit with 2 damage marked on it. The artist and liege are destroyed, and two triggers are generated from artist.
As an SBA was performed, the checks are repeated. The game now notices a 3/2 spirit with 2 damage marked on it, and the spirit is destroyed as well. More importantly, no blood artist trigger is generated, as blood artist is no longer on the battlefield.

•  Once no more state-based actions have been performed as the result of a check and no triggered abilities are waiting to be put on the stack, the appropriate player gets priority. This process also occurs during the cleanup step (see rule 514), except that if no state-based actions are performed as the result of the step's first
  check and no triggered abilities are waiting to be put on the stack, then no player gets priority and the step ends.
  

Ignore this part, it rarely matters.


This concludes the very first article in this series. If you have any question, spot an error, or something is unclear do not hesitate to contact me.

Nice work, Reinout