From the Comprehensive Rules (Commander 2018 (August 10, 2018))
- 802. Attack Multiple Players Option
- 802.1. Some multiplayer games allow the active player to attack multiple other players. If this option is used, a player can also choose to attack only one player during a particular combat.
- 802.2. As the combat phase starts, the attacking player doesn’t choose an opponent to become the defending player. Instead, all the attacking player’s opponents are defending players during the combat phase.
- 802.3. As the attacking player declares each attacking creature, they choose a defending player or a planeswalker controlled by a defending player for it to attack. See rule 508, “Declare Attackers Step.”
- 802.3a Restrictions and requirements that don’t apply to attacking a specific player are evaluated based on the entire group of attacking creatures. Restrictions and requirements that apply to attacking a specific player apply only to creatures attacking that player. The entire group of attacking creatures must still be legal. See rule 508.1.
- 802.3b Creatures in a band can’t attack different players. See rule 702.21, “Banding.”
- 802.4. If more than one player is being attacked or controls a planeswalker that’s being attacked, each defending player in APNAP order declares blockers as the declare blockers step begins. (See rule 101.4 and rule 509, “Declare Blockers Step.”) The first defending player declares all their blocks, then the second defending player, and so on.
- 802.4a A defending player can block only with creatures they control. Those creatures can block only creatures attacking that player or a planeswalker that player controls.
- 802.4b When determining whether a defending player’s blocks are legal, ignore any creatures attacking other players and any blocking creatures controlled by other players.
- 802.5. After blockers have been declared, if any creatures are blocking multiple creatures, each defending player in APNAP order announces the damage assignment order among the attacking creatures for each blocking creature they control. See rule 510, “Combat Damage Step.”
- 802.6. Combat damage is assigned in APNAP order. Other than that, the combat damage step proceeds just as in a two-player game. See rule 510, “Combat Damage Step.”
From the glossary of the Comprehensive Rules (Commander 2018 (August 10, 2018))
- Attack Multiple Players Option
- An option that may be used in certain multiplayer variants. See rule 802, “Attack Multiple Players Option.”