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Being new to MTG, I've learned that abilities from spells go to the stack and resolve in reversed order of their placement on the stack. But I haven't heard of the term state-based effects until reading Do things on the stack or state-based effects resolve between first strike and normal combat damage?

My creature deals his first strike damage, immediately killing the opponent's creature before he is able to deal combat damage as a state-based effect.

Do state-based effects refer to combat damage and creature stats, such as the amount of remaining health of the creature? And do stack-effects—if that's how it's called—refer to all triggered abilities by any spell? Am I misinterpreting and/or missing something?

I'm uncertain whether my deductions are correct, so a clear definition of state-based effects and stack-effects (including source for further reading) is much appreciated.

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Generally, if you want to learn about the rules in-depth, you can check the current, official rules, either the basic rulebook, or the comprehensive rules that include everything but are intended to be read to look up specific details rather than from beginning to end.

State-based actions are a set of rules that are automatically checked throughout the game, specifically whenever a player would gain priority (the right to take actions like casting spells, playing lands, etc.). Among others, they make players lose to lack of life points, cause creatures to die to lethal damage or zero toughness, make you put identical legendaries into the graveyard, and kill auras that are not attached to anything. They cannot be reacted to in any way. You can find the full list of state-based actions in section 704 of the Comprehensive Rules.

Spells and abilities on the stack (not effects) are just that. As you noted, they resolve in reverse order and have effects such as dealing damage or drawing cards. Whenever a spell or ability has finished resolving, the active player (the player whose turn it is) gets priority, which, as mentioned above, causes state-based actions to be checked first.

Abilities are represented by the text on cards. The four types of abilities are

  • Spell ability: an effect that happens as an instant or sorcery spell resolves
  • Activated ability: pay a cost do put an ability on the stack
  • Triggered ability: creates an ability on the stack whenever a specific event happens
  • Static ability: creates a continuous effect that is always active

Spell abilities only appear on instants and sorceries, and while instants and sorceries can have all four types of abilities, the overwhelming majority of instants and sorceries have only spell abilities. Other objects such as permanents on the battlefield can have activated, triggered, or static abilities.

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State-based actions are things that the game causes to happen automatically.

Each time a player would get priority (when a player is able to act), the game first checks to see if there is anything that needs to happen.

There is a list of a total of 24 things that the game checks for (though the last 5 only happen in special types of games, like Commander or Two-Headed Giant, so only 19 things in a normal game).

Without listing all 24 of them, because that isn't generally useful for a new player, the common state-based actions that you encounter all the time are things like:

  • A player with 0 or less life loses the game
  • A player with 10 or more poison counters loses the game
  • A player who tried to draw from an empty library loses the game
  • A creature with 0 or less toughness is moved to the graveyard (does not count as destroyed)
  • A creature with at least as much damage as toughness is destroyed

Basically, state-based actions are what cause things like taking to much damage to actually destroy a creature.

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The thing is, state-based actions (SBA) do not use the stack unlike effects, and they always take priority whenever they're checked (which is every time when resolving a spell or ability).

E.g.: I control a Sage of Ancient Lore and a Niv-Mizzet, Parun, and my opponent casts a Windfall while I have two cards in hand. SBA's are checked, I'd draw a card due to Niv's ability, SBA's are checked, then the Windfall would be resolved, I'd discard three cards and draw three cards, Niv's ability would be put thrice on the stack and then SBA's are checked. Then, before and after each time it resolves, SBA's are checked.

As you can see, SBA's are quite the invisible ones as you don't usually declare them being checked through the game. Also, if a SBA would trigger an effect, much like when playing lands or turning a morph face-up, only the trigger is put on the stack.

E.g.: I control a Laboratory Maniac and I draw the last card on my library. Then, SBA's are checked and the game says "you drew the last card on your library, you lose the game" but the Maniac says "before that, my ability triggers. Your draw on an empty library which I replace with winning the game."

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    Lab maniac is a replacement effect, not a triggered ability – Caleth Jun 13 at 10:16
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    Right, and you don't lose when you draw the last card in your library, you lose if you tried to draw a card while your library was empty. With Maniac, you never actually try to draw that card, and you win instead. All of this would happen before SBAs are checked. – GendoIkari Jun 13 at 16:45
  • True. Too much time playing Dragon Ball – Phazoning Jun 13 at 16:46
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Do state-based effects refer to combat damage and creature stats, such as the amount of remaining health of the creature?

The term is SBA, for State Based Actions. "SBA" refers to actions taken on the basis of the state, not the state itself. Damage and stats are states, not actions. One SBA is checking whether the total damage is greater than or equal to the toughness, and if so (assuming it's not indestructible), sending the creature to the graveyard. The sending to the graveyard is an action. The creature having more damage than toughness is not an action, it's a state.

In programming terms:

  def check_damage(creature):
       if creature.toughness <= creature.damage and not "indestructible" in creature.abilities:
            creature.destroyed()

check_damage is a function (action) that takes variables (state) as input.

Also, there isn't actually any concept of creature "health" in MtG, although Arena does deduct damage from toughness as if there were.

And do stack-effects—if that's how it's called—refer to all triggered abilities by any spell?

Not all abilities use the stack. The main example is mana abilities. Generally, however, spells and triggered or activated abilities are put on the stack. And generally only permanents put abilities on the stack, not spells (although spells can put a permanent on the battlefield, and that permanent can then have abilities). So for instance, if you cast Serra Angel, then you put Serra Angel on the stack. Until it resolves, it's a spell, not a permanent. When it resolves, you put a Serra Angel onto the battlefield, at which point it's a permanent. Serra Angel the permanent has the ability "Vigilance", Serra Angel the spell does not. There are a few abilities, such as "Can't be Countered" that do apply while a spell is on the stack.

  • Your thorough explanation is much appreciated, you've managed to fill some blanks and question marks! – Lainathiel Jun 13 at 16:56
  • Your last paragraph is a little confusing. You start by talking about exceptions to the "activated abilities go on the stack" rule, then you transition to taking about static abilities, which are really a completely separate category of ability. And it's not accurate to say that abilities only exist in certain zones. Serra Angel the card has Vigilance no matter what zone it's in; the ability just doesn't do anything except on the battlefield. – murgatroid99 Jun 13 at 17:29
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There are two differences: speed and origin.

In terms of speed, state-based actions are faster than anything that uses the stack because they are checked, among other times, in between each spell/ability on the stack resolving1. Let's say you are at 3 life and cast Heroes Remembered. In response, your opponent casts Lightning Bolt, targeting you. Lightning Bolt resolves first, causing you to go to 0 life. Even though you are about to gain 20 life, state-based actions are checked before your spell resolves and you lose the game from having 0 or less life (CR 704.5a).

In terms of origin, state-based actions come from the game rules where things on the stack come from the cards you play with. When you kill a Storm Crow with a Lightning Bolt, this is a combination of a spell on the stack and a state based action. You cast the spell Lightning Blot and it goes on the stack. When it resolves, Storm Crow has 3 damage marked on it. The next time a player receives priority (immediately following the resolution of Lightning Bolt), Storm Crow is destroyed by the state based actions that says a creature with damage greater than or equal to its toughness is destroyed (CR 704.5g).

1. A more complete explanation is that state-based actions are checked any time a player would receive priority (CR 704.3). This happens at least once (and possibly up to the number of players in the game if most or all players pass priority) at the beginning of most steps and phases, after a spell or ability resolves, and after a spell or ability resolves (CR 116.3). Then, if any state-based actions happened, state-based actions are checked again until none happen (CR 704.3).

Most spells and abilities use the stack, with two notable exceptions (neither of which are state-based effects): mana abilities and static abilities. Mana abilities (abilities that generate mana, do not require a target, and are not loyalty abilities) resolve immediately rather than using the stack. Static abilities meanwhile constantly affect the game.

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