Flanking

Flanking is a keyword ability that gives creatures that block a creature with flanking -1/-1, unless the blocker also has flanking. The first tournament-legal cards with this keyword were printed in the Mirage block, with a further set of Flanking cards appearing in Time Spiral block. There are currently 33 cards that have flanking or can grant it to a creature. The ability is found in all colors, but is primarily a white, red or black ability. In the Mirage block it is found on eight white creatures, four red creatures, three black creatures and one each in blue and green. In the Time Spiral block, the ability is mainly white, appearing on ten white creatures, three red creatures and one black creature.

From the ()

As this is done during the Declare Blockers Step, if a creature is put into the graveyard as a result of the -1/-1, that creature will deal no damage to the creature with Flanking, even if it has first strike. The creature with flanking is still considered blocked, however, so no damage will be dealt to defending player, unless the creature with flanking also has trample.

Flanking only triggers when a creature with flanking becomes blocked, not when it blocks.

Rulings

• This may kill the blocker prior to damage being assigned in combat, but the attacker is still blocked.
• Flanking applies to blockers which are not assigned to the Flanking creature directly. For example, creatures that become blockers due to blocking a member of a band which includes the Flanking creature are subject to the Flanking -1/-1 ability.
• Gaining Flanking after blockers are declared will have no effect on the blockers because the time for Flanking to trigger has already passed.
• If an attacking creature has multiple instances of the Flanking ability, even one instance of Flanking on the blocking creature will negate the effect.