Banding is a keyword ability.
Banding works during the Combat phase, and it works differently depending on who's attacking. Essentially, it lets multiple creatures attack/block as though they were one creature. When you attack, you can add any number of banding creatures onto one attacking creature (meaning your band can only have one non-banding creature). If one or more of your band's creatures has an evasion ability, such as Flying, Fear, or Shadow, but at least one creature in the band lacks that ability, then the entire band can still be blocked as though the ability didn't exist; in other words, a creature that could block any member of the band can block the entire band. As usual per normal rules, you can always block one creature with any number of creatures, but as long as one of the creatures has banding, the entire group blocking the creature is a band.
As long as one of the creatures has banding, you can assign combat damage to your blocking creatures as you wish. This can cancel out Trample, as lethal damage has to be assigned to all blocking creatures before it can be assigned to the player. However, this only applies to the creatures blocking one particular creature. If your opponent attacks with two creatures, you block each of them separately, and one of your blockers has banding, you cannot split the combat damage between them because your blockers are blocking separately. If your two blockers blocked one of the attacking creatures, you would be able to divide the damage as you choose.
- 702.21a Banding is a static ability that modifies the rules for combat.
- 702.21b “Bands with other” is a special form of banding. If an effect causes a permanent to lose banding, the permanent loses all “bands with other” abilities as well.
- 702.21c As a player declares attackers, he or she may declare that one or more attacking creatures with banding and up to one attacking creature without banding (even if it has “bands with other”) are all in a “band.” He or she may also declare that one or more attacking [quality] creatures with “bands with other [quality]” and any number of other attacking [quality] creatures are all in a band. A player may declare as many attacking bands as he or she wants, but each creature may be a member of only one of them. (Defending players can’t declare bands but may use banding in a different way; see rule 702.21j.)
- 702.21d All creatures in an attacking band must attack the same player or planeswalker.
- 702.21e Once an attacking band has been announced, it lasts for the rest of combat, even if something later removes banding or “bands with other” from one or more of the creatures in the band.
- 702.21f An attacking creature that’s removed from combat is also removed from the band it was in.
- 702.21g Banding doesn’t cause attacking creatures to share abilities, nor does it remove any abilities. The attacking creatures in a band are separate permanents.
- 702.21h If an attacking creature becomes blocked by a creature, each other creature in the same band as the attacking creature becomes blocked by that same blocking creature.
- Example: A player attacks with a band consisting of a creature with flying and a creature with swampwalk. The defending player, who controls a Swamp, can block the flying creature if able. If he or she does, then the creature with swampwalk will also become blocked by the blocking creature(s).
- 702.21i If one member of a band would become blocked due to an effect, the entire band becomes blocked.
- 702.21j During the combat damage step, if an attacking creature is being blocked by a creature with banding, or by both a [quality] creature with “bands with other [quality]” and another [quality] creature, the defending player (rather than the active player) chooses how the attacking creature’s damage is assigned. That player can divide that creature’s combat damage as he or she chooses among any number of creatures blocking it. This is an exception to the procedure described in rule 510.1c.
- 702.21k During the combat damage step, if a blocking creature is blocking a creature with banding, or both a [quality] creature with “bands with other [quality]” and another [quality] creature, the active player (rather than the defending player) chooses how the blocking creature’s damage is assigned. That player can divide that creature’s combat damage as he or she chooses among any number of creatures it’s blocking. This is an exception to the procedure described in rule 510.1d.
- 702.21m Multiple instances of banding on the same creature are redundant. Multiple instances of “bands with other” of the same kind on the same creature are redundant.