http://www.wizards.com/Magic/Magazine/Article.aspx?x=mtg/daily/arcana/1161

The Boros Legion marches in lockstep across the battlefield. Individually, the troops are disciplined and capable. As a unit, the battalion is nearly unstoppable. The "Rally and Rout" deck hits the ground running with cheap, aggressive creatures. But your assault really kicks into overdrive once you assemble a squad of three or more creatures. At that point, every attack is an overwhelming military exercise. Once your ground troops have softened up your opponent, your battery of long-range burn spells is more than adequate to finish the job.

The battalion mechanic is the newest addition to the Boros arsenal. Whenever you attack with three or more creatures, many of them will get powerful bonuses. Boros Elite transforms from minor annoyance to game-ending threat, and Firefist Striker can force through loads of damage by making your opponent's best creature unable to block.

Your major goal is to attack with three or more creatures as early and as often as possible, and your deck features a number of cards that support that initiative. Token makers like Gather the Townsfolk and Sunhome Guildmage provide multiple creatures with one card, which makes it much easier to maintain critical mass. Hasty creatures are surprise attackers that can quickly change the math in your favor. With a combination of haste and flying, Skyknight Legionnaire excels at attacking turn after turn.

The non-creature spells in the deck are flexible tools for maximizing your assault. Low-cost burn spells like Pillar of Flame and Searing Spear take out key blockers early on. Later, when the battlefield is crowded with blockers, you're better off pointing your damage spells directly at your opponent's life total. Similarly, Boros Charm can protect your creatures from mass removal spells or it can finish off an opponent as his or her life total dwindles.

When sideboarding, pinpoint the biggest challenge your enemy is throwing at you, then attack it with the appropriate option. If he or she is playing a slower deck with a few tough-to-kill threats, Bonds of Faith can empower one of your many Humans to end the game before your opponent's creature makes an appearance or can neutralize it once it does. War Priest of Thune can liberate your army from enchantments like Oblivion Ring or Detention Sphere. Thunderous Wrath is a big cannon shot that will take huge chunks out of your opponent's life total.

Once you're familiar with the "Rally and Rout" deck, tailor your army for unrivaled battlefield superiority. If you prefer assembling a massive army and overwhelming your opponent on all fronts, check out cards like Geist-Honored Monk from Innistrad or Assemble the Legion from Gatecrash. If you'd prefer addressing opposing threats directly, try Firemane Avenger from Gatecrash. It's a 3/3 flier that can deal 3 damage to a target each time it attacks with a squad, proving that sometimes the best defense is a good offense.