508.1.
First, the active player declares attackers. This turn-based action doesn‘t use the stack. To
declare attackers, the active player follows the steps below, in order. If at any point during the
declaration of attackers, the active player is unable to comply with any of the steps listed below, the
declaration is illegal; the game returns to the moment before the declaration (see rule 717,
«Handling Illegal Actions»).
508.1a
The active player chooses which creatures that he or she controls, if any, will attack. The
chosen creatures must be untapped, and each one must either have haste or have been controlled
by the active player continuously since the turn began.
508.1b
If the defending player controls any planeswalkers, or the game allows the active player to
attack multiple other players, the active player announces which player or planeswalker each of
the chosen creatures is attacking.
508.1c
The active player checks each creature he or she controls to see whether it‘s affected by any
restrictions (effects that say a creature can‘t attack, or that it can‘t attack unless some condition
is met). If any restrictions are being disobeyed, the declaration of attackers is illegal.
Example: A player controls two creatures, each with a restriction that states “[This
creature] can?t attack alone.” It?s legal to declare both as attackers.
508.1d
The active player checks each creature he or she controls to see whether it‘s affected by any
requirements (effects that say a creature must attack, or that it must attack if some condition is
met). If the number of requirements that are being obeyed is fewer than the maximum possible
number of requirements that could be obeyed without disobeying any restrictions, the
declaration of attackers is illegal. If a creature can‘t attack unless a player pays a cost, that
player is not required to pay that cost, even if attacking with that creature would increase the
number of requirements being obeyed.
Example: A player controls two creatures: one that “attacks if able” and one with no
abilities. An effect states “No more than one creature can attack each turn.” The only
legal attack is for just the creature that “attacks if able” to attack. It?s illegal to attack
with the other creature, attack with both, or attack with neither.
508.1e
If any of the chosen creatures have banding or a «bands with other» ability, the active player
announces which creatures, if any, are banded with which. (See rule 702.20, «Banding.»)
508.1f
The active player taps the chosen creatures. Tapping a creature when it‘s declared as an
attacker isn‘t a cost; attacking simply causes creatures to become tapped.
508.1g
If any of the chosen creatures require paying costs to attack, the active player determines the
total cost to attack. Costs may include paying mana, tapping permanents, sacrificing
permanents, discarding cards, and so on. Once the total cost is determined, it becomes «locked
in.» If effects would change the total cost after this time, ignore this change.
508.1h
If any of the costs require mana, the active player then has a chance to activate mana
abilities (see rule 605, «Mana Abilities»).
508.1i
Once the player has enough mana in his or her mana pool, he or she pays all costs in any
order. Partial payments are not allowed.
508.1j
Each chosen creature still controlled by the active player becomes an attacking creature. It
remains an attacking creature until it‘s removed from combat or the combat phase ends,
whichever comes first. See rule 506.4.
508.2.
Second, any abilities that triggered on attackers being declared go on the stack. (See rule 603,
«Handling Triggered Abilities.»)
508.2a
Abilities that trigger on a creature attacking trigger only at the point the creature is declared
as an attacker. They will not trigger if a creature attacks and then that creature‘s characteristics
change to match the ability‘s trigger condition.
Example: A permanent has the ability “Whenever a green creature attacks, destroy that
creature at end of combat.” If a blue creature attacks and is later turned green, the
ability will not trigger.
508.3.
Third, the active player gets priority. Players may cast spells and activate abilities.
508.4.
If a creature is put onto the battlefield attacking, its controller chooses which defending player or
which planeswalker a defending player controls it‘s attacking as it enters the battlefield (unless the
effect that put it onto the battlefield specifies what it‘s attacking). Such creatures are «attacking»
but, for the purposes of trigger events and effects, they never «attacked.»
508.4a
If the effect that put a creature onto the battlefield attacking specifies it‘s attacking a certain
player, and that player is no longer in the game when the effect resolves, the creature is put onto
the battlefield but is never considered an attacking creature. The same is true if the effect
specifies a creature is put onto the battlefield attacking a planeswalker and that planeswalker is
no longer on the battlefield or is no longer a planeswalker when the effect resolves.
508.5.
If an ability of an attacking creature refers to a defending player, or a spell or ability refers to
both an attacking creature and a defending player, then unless otherwise specified, the defending
player it‘s referring to is the player that creature was attacking at the time it became an attacking
creature that combat, or the controller of the planeswalker that creature was attacking at the time it
became an attacking creature that combat.
508.5a
In a multiplayer game, any rule, object, or effect that refers to a «defending player» refers to
one specific defending player, not to all of the defending players. If a spell or ability could apply
to multiple attacking creatures, the appropriate defending player is individually determined for
each of those attacking creatures. If there are multiple defending players that could be chosen,
the controller of the spell or ability chooses one.
508.6.
If no creatures are declared as attackers or put onto the battlefield attacking, skip the declare
blockers and combat damage steps.