The Stack

Fblthp, the Lost card art

I have mentioned the stack several times in this blog, but never explained it. I do so today.

Magic's official rules describe this concept in detail. The word is used 416 times in that document, showing its importance. Some basics, quoted or paraphrased from the rules:

The stack is a zone. A zone is a place where objects can be during a game. There are "seven zones in Magic: library, hand, battlefield, graveyard, stack, exile, and command. Each player has their own library, hand, and graveyard. The other zones are shared by all players." (Rule 400.1)

Section 405 focuses on the stack. Relevant portions from that section:

405.1. When a spell is cast, the physical card is put on the stack. When an ability is activated or triggers, it goes on top of the stack without any card associated with it. 

405.2. The stack keeps track of the order that spells and/or abilities were added to it. Each time an object is put on the stack, it’s put on top of all objects already there. 

405.3. If an effect puts two or more objects on the stack at the same time, those controlled by the active player are put on lowest, followed by each other player’s objects in APNAP order. If a player controls more than one of these objects, that player chooses their relative order on the stack. 

405.5. When all players pass in succession, the top (last-added) spell or ability on the stack resolves. If the stack is empty when all players pass, the current step or phase ends and the next begins.

Note: "APNAP order" above means "Active Player, Non-Active Player." The active player is whose turn it is; the non-active players go in turn order [clockwise] from that player. I'll cover that another time.

Spells and activated/triggered abilities remain on the stack until they are resolved, countered, or otherwise leave the stack (see rules 112 and 113). 

Summarizing, the stack is a "first in, last out" concept where players stack spells and abilities until everyone has passed. Then the topmost spell/ability is resolved, then the next, and so on until the stack is empty. The stack exists in all steps/phases of the game. In a given phase, the active player has priority to put something on the stack first; if they pass, then the non-active players can choose to do the same. If they pass, then the game proceeds to the next phase.

Two things to note:

1) Most counterspells in the game counter spells. Note that "Activated and triggered abilities on the stack aren’t spells, and therefore can’t be countered by anything that counters only spells. Activated and triggered abilities on the stack can be countered by effects that specifically counter abilities. Static abilities don’t use the stack and thus can’t be countered at all." (Rule 113.9)

2) Some things that happen during the game don’t use the stack (405.6). Summarizing this section, these are:

- effects (the result of spells and abilities resolving)

- mana abilities (I cover this in a different post)

- special actions (rule 116)

- turn-based and state-based actions (see rule 703 and 704)

- a player conceding the game [this one is hilarious. Imagine if "I concede" would go on the stack, and someone else could counter it. "No you don't. Sit down."]

Example 1:

The simplest (and most common) example are two spells. I cast Hurloon Minotaur; that goes on the stack. My opponent casts Cancel; that goes on top of the stack. 

I have a chance to respond but pass; my opponent passes, too. Then the spells on the stack are resolved top to bottom: Cancel resolves, targeting Hurloon Minotaur. My minotaur spell is canceled and goes to my graveyard [sob].

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Example 2:

Order matters greatly. Here, I have a Grizzly Bears on the battlefield and declare it as an attacker, tapping it to do so. I pass priority and my opponent casts Cut Down targeting it. I have priority again. In response, I cast Giant Growth. To the stack is (top to bottom) Giant Growth, Cut Down.

Everyone passes. Giant Growth resolves, making the Grizzly Bears 5/5 until end of turn. Cut Down then resolves, but has no target, because Grizzly Bears now have a total power and toughness greater than 5. The spell 'fizzles' and nothing happens (it goes to the graveyard). Grizzly Bears attacks as a 5/5.

Now let's reverse the order. I attack with my Grizzly Bears, and (having priority) choose to cast Giant Growth right away. My opponent, in response, casts Cut Down. Now the stack is (top to bottom) Cut Down, Giant Growth. Everyone passes. Cut Down resolves, and the Grizzly Bears is destroyed (and put in the graveyard). Giant Growth then resolves, but has no target, because Grizzly Bears is no longer there. The spell 'fizzles' and nothing happens (it goes to the graveyard). There is no attack.

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In these simple examples, the stack is straightforward. But things can get complicated quickly, especially when you throw abilities and multiple players into the mix. 

Seasoned Magic players don't say "I put [x] on the stack." They'll say, instead, something like "I play Hurloon Minotaur" and expect that anyone who wants to respond will speak up ("in response, I ___") and do so at that time. If nobody does, it resolves and enters the battlefield.

The stack is important to understand, even if it goes unmentioned in most Magic games. It is a key part of the game's strategy, enabling the interactions that make the game so exciting, challenging, and fun.