811.2b Exactly one of the attack left, attack right, and attack multiple players options must be used. See rule 803, “Attack Left and Attack Right Options,” and rule 802, “Attack Multiple Players Option.”
811.4 A player can’t attack opponents who aren’t seated next to them, planeswalkers that aren’t controlled by opponents seated next to them, or battles that aren’t protected by opponents seated next to them.
811.5 In the Alternating Teams variant, a team’s resources (cards in hand, mana, and so on) are not shared. Teammates can’t review each other’s hands unless they are sitting next to each other. Teammates may discuss strategies at any time. Teammates can’t manipulate each other’s cards or permanents.