509.1.
First, the defending player declares blockers. This turn-based action doesn‘t use the stack. To
declare blockers, the defending player follows the steps below, in order. If at any point during the
declaration of blockers, the defending 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»).
509.1a
The defending player chooses which creatures that he or she controls, if any, will block. The
chosen creatures must be untapped. For each of the chosen creatures, the defending player
chooses one creature for it to block that‘s attacking him, her, or a planeswalker he or she
controls.
509.1b
The defending player checks each creature he or she controls to see whether it‘s affected by
any restrictions (effects that say a creature can‘t block, or that it can‘t block unless some
condition is met). If any restrictions are being disobeyed, the declaration of blockers is illegal.
A restriction may be created by an evasion ability (a static ability an attacking creature has
that restricts what can block it). If an attacking creature gains or loses an evasion ability after a
legal block has been declared, it doesn‘t affect that block. Different evasion abilities are
cumulative.
Example: An attacking creature with flying and shadow can?t be blocked by a creature
with flying but without shadow.
509.1c
The defending player checks each creature he or she controls to see whether it‘s affected by
any requirements (effects that say a creature must block, or that it must block 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 blockers is illegal. If a creature can‘t block unless a player pays a cost, that player
is not required to pay that cost, even if blocking with that creature would increase the number of
requirements being obeyed.
Example: A player controls one creature that “blocks if able” and another creature
with no abilities. An effect states “Creatures can?t be blocked except by two or more
creatures.” Having only the first creature block violates the restriction. Having neither
creature block fulfills the restriction but not the requirement. Having both creatures
block the same attacking creature fulfills both the restriction and the requirement, so
that?s the only option.
509.1d
If any of the chosen creatures require paying costs to block, the defending player determines
the total cost to block. 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.
509.1e
If any of the costs require mana, the defending player then has a chance to activate mana
abilities (see rule 605, «Mana Abilities»).
509.1f
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.
509.1g
Each chosen creature still controlled by the defending player becomes a blocking creature.
Each one is blocking the attacking creatures chosen for it. It remains a blocking creature until
it‘s removed from combat or the combat phase ends, whichever comes first. See rule 506.4.
509.1h
An attacking creature with one or more creatures declared as blockers for it becomes a
blocked creature; one with no creatures declared as blockers for it becomes an unblocked
creature. This remains unchanged until the creature is removed from combat, an effect says that
it becomes blocked or unblocked, or the combat phase ends, whichever comes first. A creature
remains blocked even if all the creatures blocking it are removed from combat.
509.2.
Second, for each attacking creature that‘s become blocked, the active player announces that
creature‘s damage assignment order, which consists of the creatures blocking it in an order of that
player‘s choice. (During the combat damage step, an attacking creature can‘t assign combat damage
to a creature that‘s blocking it unless each creature ahead of that blocking creature in its order is
assigned lethal damage.) This turn-based action doesn‘t use the stack.
Example: Vastwood Gorger is blocked by Llanowar Elves, Runeclaw Bear, and Serra
Angel. Vastwood Gorger?s controller announces the Vastwood Gorger?s damage
assignment order as Serra Angel, then Llanowar Elves, then Runeclaw Bear.
509.2a
During the declare blockers step, if a blocking creature is removed from combat or a spell or
ability causes it to stop blocking an attacking creature, the blocking creature is removed from all
relevant damage assignment orders. The relative order among the remaining blocking creatures
is unchanged.
509.3.
Third, for each blocking creature, the defending player announces that creature‘s damage
assignment order, which consists of the creatures it‘s blocking in an order of that player‘s choice.
(During the combat damage step, a blocking creature can‘t assign combat damage to a creature it‘s
blocking unless each creature ahead of that blocked creature in its order is assigned lethal damage.)
This turn-based action doesn‘t use the stack.
509.3a
During the declare blockers step, if an attacking creature is removed from combat or a spell
or ability causes it to stop being blocked by a blocking creature, the attacking creature is
removed from all relevant damage assignment orders. The relative order among the remaining
attacking creatures is unchanged.
509.4.
Fourth, any abilities that triggered on blockers being declared go on the stack. (See rule 603,
«Handling Triggered Abilities.»)
509.4a
An ability that reads «Whenever [this creature] blocks, . . .» generally triggers only once
each combat for that creature, even if it blocks multiple creatures. It triggers if the creature is
declared as a blocker. It will also trigger if that creature becomes a blocker as the result of an
effect, but only if it wasn‘t a blocking creature at that time. (See rule 509.1g.) It won‘t trigger if
the creature is put onto the battlefield blocking.
509.4b
An ability that reads «Whenever [this creature] blocks a creature, . . .» triggers once for each
attacking creature the creature with the ability blocks. It triggers if the creature is declared as a
blocker. It will also trigger if an effect causes that creature to block an attacking creature, but
only if it wasn‘t already blocking that attacking creature at that time. It won‘t trigger if the
creature is put onto the battlefield blocking.
509.4c
An ability that reads «Whenever [this creature] becomes blocked, . . .» generally triggers
only once each combat for that creature, even if it‘s blocked by multiple creatures. It will trigger
if that creature becomes blocked by at least one creature declared as a blocker. It will also
trigger if that creature becomes blocked by an effect or by a creature that‘s put onto the
battlefield as a blocker, but only if the attacking creature was an unblocked creature at that time.
(See rule 509.1h.)
509.4d
An ability that reads «Whenever [this creature] becomes blocked by a creature, . . .» triggers
once for each creature that blocks the named creature. It triggers if a creature is declared as a
blocker for the attacking creature. It will also trigger if an effect causes a creature to block the
attacking creature, but only if it wasn‘t already blocking that attacking creature at that time. In
addition, it will trigger if a creature is put onto the battlefield blocking that creature. It won‘t
trigger if the creature becomes blocked by an effect rather than a creature.
509.4e
If an ability triggers when a creature blocks or becomes blocked by a particular number of
creatures, the ability triggers if the creature blocks or is blocked by that many creatures when
blockers are declared. Effects that add or remove blockers can also cause such abilities to
trigger. This applies to abilities that trigger on a creature blocking or being blocked by at least a
certain number of creatures as well.
509.4f
If an ability triggers when a creature with certain characteristics blocks, it will trigger only if
the creature has those characteristics at the point blockers are declared, or at the point an effect
causes it to block. If an ability triggers when a creature with certain characteristics becomes
blocked, it will trigger only if the creature has those characteristics at the point it becomes a
blocked creature. If an ability triggers when a creature becomes blocked by a creature with
certain characteristics, it will trigger only if the latter creature has those characteristics at the
point it becomes a blocking creature. None of those abilities will trigger if the relevant
creature‘s characteristics change to match the ability‘s trigger condition later on.
Example: A creature has the ability “Whenever this creature becomes blocked by a
white creature, destroy that creature at end of combat.” If the creature becomes blocked
by a black creature that is later turned white, the ability will not trigger.
509.4g
An ability that reads «Whenever [this creature] attacks and isn‘t blocked, . . .» triggers if no
creatures are declared as blockers for that creature. It won‘t trigger if the attacking creature is
blocked and then all its blockers are removed from combat.
509.5.
Fifth, the active player gets priority. Players may cast spells and activate abilities.
509.6.
If a spell or ability causes a creature on the battlefield to block an attacking creature, the active
player announces the blocking creature‘s placement in the attacking creature‘s damage assignment
order. The relative order among the remaining blocking creatures is unchanged. Then the defending
player announces the attacking creature‘s placement in the blocking creature‘s damage assignment
order. The relative order among the remaining attacking creatures is unchanged. This is done as part
of the blocking effect.
509.7.
If a creature is put onto the battlefield blocking, its controller chooses which attacking creature
it‘s blocking as it enters the battlefield (unless the effect that put it onto the battlefield specifies
what it‘s blocking), then the active player announces the new creature‘s placement in the blocked
creature‘s damage assignment order. The relative order among the remaining blocking creatures is
unchanged. A creature put onto the battlefield this way is «blocking» but, for the purposes of trigger
events and effects, it never «blocked.»
Example: Giant Spider is blocked by Canyon Minotaur. The defending player casts Flash
Foliage, which puts a Saproling token onto the battlefield blocking the Giant Spider. Giant
Spider?s controller announces the Giant Spider?s damage assignment order as the Saproling
token, then Canyon Minotaur.