Instant, 2{R/W}{R/W} (4) ({R/W} can be paid with either {R} or {W}.) Cast Master Warcraft only before attackers are declared. You choose which creatures attack this turn. You choose how each creature blocks this turn.1
Illus. Zoltan Boros & Gabor Szikszai
10/1/2005: You choose attackers and make blocking assignments regardless of whether it's your turn and regardless of whether the creatures are attacking you. Your choices must be legal within the normal rules for attacking and blocking.
10/1/2005: If an additional combat phase has been created, you may, if you choose, cast Master Warcraft after attackers have been declared during the first combat phase but before attackers have been declared during the second one.
1/1/2006: You can decide that a creature won't block.
4/1/2008: If the defending player controls a planeswalker, the person who cast Master Warcraft first chooses the complete group of creatures that are going to attack. Then, for each of those creatures, the active player chooses who or what it's going to attack.
Ravnica: City of Guilds
(Rare)